A Muslim tried to prove the authenticity of the Gospel of Barnabas. To do so, he searched the writings of the church fathers. He said that Pope John Chrysostom was one of them! John Chrysostom said in his commentary on Matthew 5: 39 “fire is not quenched by another, but fire by water.” The writer of Gospel of Barnabas said that Jesus said “Fire is not extinguished with fire, but rather with water; even so I say unto you that ye shall not overcome evil with evil, but rather with good” The Muslim has another example but by saint Augustine. If you say that the writer of Gospel of Barnabas quotes from John, he may say why can’t you say that concerning the writings of Justin Martyr, Irenaeus, etc.
All this “proves” is that the Muslims have an agenda to try to prove that the supposed “Gospel of Barnabas” is genuine, which it certainly is not. It is ironic that your Muslim friend claims that John Chrysostom was a pope, as he never lived in or even visited Rome. He was a leader of the churches in Asia Minor, and is a father of the Orthodox, not the Roman Church.
Who is a more famous author, John Chrysostom or the (unknown) author of the falsely-attributed “Gospel of Barnabas”? Who is a more famous author, Augustine or the obscure, unknown author of the Gospel of Barnabas? Let us assume for a moment, just for the sake of argument, that we do not know when the Gospel of Barnabas was written (We do, and it was about twelve centuries after Chrysostom, but never mind that), which is more logical, that the incredibly famous Chrysostom quoted from the unknown author of a single obscure “Gospel of Barnabas”, or that the unknown author of the obscure document quoted from the very famous John Chrysostom? The same can be said of Augustine. The answer is clear. It is far more reasonable to think that the Gospel of Barnabas is a quote from the more famous author.
Besides, to be honest, the fact that the Gospel of Barnabas has this phrase, does not prove that he got it from Chrysostom. This is a fairly obvious metaphor, which has probably been thought of dozens of times throughout the ages, as it is a fairly obvious metaphor to draw from Matthew 5:39. But never mind that.
To summarize, let us make two assumptions, one of which is very far-fetched, and the other which is not likely true:
- That we are not sure which was written first, Chrysostom’s writings or the Epistle of Barnabas.
- That one of these was actually quoting the other, rather than simply inventing a fairly obvious metaphor to use.
If we make these two assumptions, then it is far more likely that the Epistle of Barnabas quotes Chrysostom than vice verse. Rather than being proof that this book is genuine, it proves nothing at all. Realistically, it is not even a weak, never mind a strong evidence that the Epistle of Barnabas was written in ancient times.
Besides all this, as you already know (and as any honest Muslim apologist also knows) all the evidence we have points to the Gospel of Barnabas being a forgery of the very late Middle Ages. There is no evidence that there existed a Greek version of this book. The earliest manuscript was in Italian or Spanish. This argument is agenda-based, not evidence-based. I am including information below from wikipedia about this document. Here is the short version. There is absolutely no evidence that it was written before about AD 1500. It is clearly a forgery, intended to support a Muslim interpretation of Christianity. Only a closed-minded person with an agenda (in this case to make it appear that the Qur’an is right and the four gospels are wrong on Jesus’ claims about himself and on his crucifixion) would conclude anything different, and the examples from Chrysostom and Augustine do nothing to change that.
Here, I am borrowing from wikipedia:
The earliest reference to a Barnabas gospel, which is generally agreed to correspond with the one found in the two known manuscripts, is in Morisco manuscript BNM MS 9653 in Madrid, written about 1634 by Ibrahim al-Taybili in Tunisia. While describing how the Bible predicts Muhammad, he speaks of the “Gospel of Saint Barnabas where one can find the light” (“y así mismo en Evangelio de San Bernabé, donde se hallará la luz”). The first published account of the Gospel was in 1717, when a brief reference to the Spanish text is found in De religione Mohamedica by Adriaan Reland; and then in 1718, a much more detailed description of the Italian text by the Irish deist John Toland. Both Italian and Spanish texts are referred to in 1734 by George Sale in The Preliminary Discourse to the Koran:
The Muhammadans have also a Gospel in Arabic, attributed to saint Barnabas, wherein the history of Jesus Christ is related in a manner very different from what we find in the true Gospels, and correspondent to those traditions which Muhammad has followed in his Quran. Of this Gospel the Moriscoes in Africa have a translation in Spanish; and there is in the library of Prince Eugene of Savoy, a manuscript of some antiquity, containing an Italian translation of the same Gospel, made, it is to be supposed, for the use of renegades. This book appears to be no original forgery of the Muhammadans, though they have no doubt interpolated and altered it since, the better to serve their purpose; and in particular, instead of the Paraclete or Comforter, they have, in this apocryphal gospel, inserted the word Periclyte, that is, the famous or illustrious, by which they pretend their prophet was foretold by name, that being the signification of Muhammad in Arabic; and this they say to justify that passage in the Quran where Jesus Christ is formally asserted to have foretold his coming under his other name Ahmed, which is derived from the same root as Muhammad and of the same import.
Sale’s translation of the Qur’an text became the standard English version at that time; and through its dissemination, and that of the Preliminary Discourse, an awareness of the Gospel of Barnabas spread widely in scholarly circles; prompting many fruitless attempts to find the Arabic original to which Sale referred. However, in his description of the Gospel in the Preliminary Discourse, Sale was relying entirely on second-hand accounts. For example, contrary to Sale’s notice, the words paraclete or periclyte are not explicitly found in the text of either the Spanish or Italian versions; although the Greek term periclyte is transliterated into Arabic in one of the marginal notes to the Italian manuscript at Chapter 44, as a gloss to the Italian ‘uno splendore’ which is indeed there applied to Muhammad by name. Subsequent to the preparation of the Preliminary Discourse, Sale was able to borrow the Spanish manuscript itself and had a transcript made.
Earlier occurrences of a Gospel of Barnabas
A “Gospel according to Barnabas” is mentioned in two early Christian lists of “Apocrypha” works: the Latin text of Decretum Gelasianum(6th century), as well as a 7th-century Greek List of the Sixty Books. These lists are independent witnesses. In 1698 John Ernest Grabefound an otherwise unreported saying of Jesus, attributed to the Apostle Barnabas, amongst the Greek manuscripts in the Baroccian collection in the Bodleian Library; which he speculated might be a quotation from this “lost gospel”. John Toland translates the quotation as, The Apostle Barnabas says, he gets the worst of it who overcomes in evil contentions; because he thus comes to have the more sin; and claimed to have identified a corresponding phrase when he examined the surviving Italian manuscript of the Gospel of Barnabas in Amsterdam before 1709. Subsequent scholars examining the Italian and Spanish texts have been unable, however, to confirm Toland’s observation.
This work should not be confused also with the surviving Epistle of Barnabas, which may have been written in 2nd century Alexandria. There is no link between the two books in style, content, or history other than their attribution to Barnabas. On the issue of circumcision, the books clearly hold very different views, that of the epistle’s rejection of the Jewishpractice as opposed to the gospel’s promotion of the same. Neither should it be confused with the surviving Acts of Barnabas, which narrates an account of Barnabas’ travels, martyrdom and burial, and which is generally thought to have been written in Cyprus sometime after 431.
In A.D. 478, during the reign of the Eastern Roman (later Byzantine) Emperor Zeno, archbishop Anthemios of Cyprus announced that the hidden burial place of Barnabas had been revealed to him in a dream. The saint’s body was claimed to have been discovered in a cave with a copy of the canonical Gospel of Matthew on its breast; according to the contemporary account of Theodorus Lector, who reports that both bones and gospel book were presented by Anthemios to the emperor. Some scholars who maintain the antiquity of the Gospel of Barnabas propose that the text purportedly discovered in 478 should be identified with the Gospel of Barnabas instead; but this supposition is at variance with an account of Anthemios’s gospel book by Severus of Antioch, who reported having examined the manuscript around the year 500, seeking to find whether it supported the piercing of the crucified Jesus by a spear at Matthew 27:49 (it did not). According to the 11th-century Byzantine historian Georgios Kedrenos, an uncial manuscript of Matthew’s Gospel, believed to be that found by Anthemios, was then still preserved in the Chapel of St Stephen in the imperial palace in Constantinople.
View of the Austrian Imperial Library, where the Italian manuscript was kept
Prince Eugene’s Italian manuscript had been presented to him in 1713 by John Frederick Cramer (1664-1715); and was transferred to the Austrian National Library in Vienna in 1738 with the rest of his library. In Amsterdam sometime before 1709, Cramer had lent the manuscript to Toland, who writes that; (Mr. Cramer) had it out of the library of a person of great name and authority in that said city; who during his life was often heard to put a high value on the piece. Whether as a rarity, or as the model of his religion, I know not. Michel Fremaux reports no success in tracking and identifying this previous owner, or in finding a corresponding manuscript listed in any Amsterdam catalogue or inventory. However, Toland’s notice would imply that the unnamed deceased former owner was a prominent anti-Trinitarian or Unitarian by religion; and Fremaux conjectures that the manuscript may have been brought to Amsterdam by Christopher Sandius (1644-1680), either from his own activity as a collector in Poland; or more likely from his acquisition of the papers of Giovanni Michele Bruto (1517-1592), who had assembled an extensive collection of manuscript sources in Hungary and Transylvania. Cramer had published an edition of Bruto’s theological writings in 1698, and Fremaux speculates that Cramer might have come across the Gospel of Barnabas in the course of his researches within Sandius’s library in Amsterdam. Otherwise, Slomp has proposed that Gregorio Leti (1630–1701), whose Amsterdam library had been auctioned-off following his death, could be the unnamed former owner of the Italian manuscript. Leti however, though hostile to the Papacy (and Sixtus V in particular) was an orthodox Calvinist in religion.
The Italian manuscript has 506 pages, of which the Gospel of Barnabas fills pages 43 to 500, written within red frames in an Islamic style. The preceding pages five to forty-two are also red framed; but remain blank (other than for Cramer’s presentation to Prince Eugene), and it may be inferred that some sort of preface or preliminary text was intended, although the space is much greater than would have been needed for the text of the corresponding Spanish Preface. There are chapter rubrics and margin notes in ungrammatical Arabic; with an occasional Turkish word, and many Turkish syntactical features. Its binding is Turkish, and appears to be original; but the paper has an Italian watermark,which has been dated between 1563 and 1620. The same scribe wrote both the Italian text and the Arabic notes, and was clearly “occidental” in being accustomed to write from left to right. There are catchwords at the bottom of each page, a practice common in manuscripts intended to be set up for printing. The manuscript appears to be unfinished, in that the Prologue and 222 chapters are provided throughout with framed blank spaces for titular headings, but only 28 of these spaces have been filled. This Italian manuscript formed the basis for the most commonly circulated English version, a translation undertaken by Lonsdale and Laura Ragg and published in 1907. The Raggs’ English version was quickly re-translated into Arabic by Rashid Rida, in an edition published in Egypt in 1908.
The Italian spelling is idiosyncratic in frequently doubling consonants and adding an intrusive initial “h” where a word starts with a vowel (e.g. “hanno” for “anno”). The writer is not a professional scribe. Otherwise, however, the orthography and punctuation indicates a hand formed in the first half of the 16th century, and in certain key respects is characteristically Venetian. The underlying dialect however, is Tuscan; and shows a number of characteristic late medieval (14th–15th-century) forms. The linguistic experts consulted by the Raggs concluded that the Vienna manuscript was most likely the work of an older Venetian scribe, copying a Tuscan original, and writing in the second half of the 16th century.
Church of St Barnabas in Marino, Italy. The Spanish manuscript purports to have been sourced from a ‘Fra Marino’, supposedly the pseudonym of a high-ranking Roman ecclesiastic.
Sale says of the lost Spanish manuscript; The book is a moderate quarto.. written in a very legible hand, but a little damaged towards the latter end. It contains two hundred and twenty-two chapters of unequal length, and four hundred and twenty pages. It had been lent to Sale by Dr. George Holme (1676-1765), Rector of Headley in Hampshire from 1718 till his death. Sale had a transcript made for his own use, and returned the original to Dr Holme; and it is recorded as being bequeathed to Queen’s College, Oxford in Holme’s will. This manuscript, with an English translation, passed subsequently to Dr. Thomas Monkhouse, also of Queen’s College, who himself lent both text and translation to Dr. Joseph White who used them for his series of Bampton Lectures in 1784. Sale supposes that the Spanish manuscript is African in origin, but otherwise provides no indication of how Dr. Holme might have come by it; but as Holme had been chaplain to the English factory in Algiers from 1707 to 1709, a North African provenance may be inferred. Sale quotes three passages from the text in Spanish; and a further nine chapters are quoted by White in English translation. No trace is known of the original Spanish manuscript after Dr. Monkhouse’s death in 1792.
However, an 18th-century copy, derived from the manuscript, was mentioned in a 1760 catalogue of the collection of manuscripts of the deceased author Joseph Ames, where it was described as El Evangelio de Barnabas Apostol, transcribed from one in the Possession of Mr. Edm. Calamy, who bought it at the Decease of Mr. Geo. Sale, fol. Then, William Hone mentions the manuscript at the end of his 1823 book Ancient mysteries described, where Hone describes why he did not include the Gospel of Barnabas in his other book, Apocryphal New Testament:
It is said that the Gospel of Barnabas ought to have been included. Of that Gospel, the Rev. Jeremiah Jones supposed that there were no fragments extant. He refers to the Italian MS. of it in Prince Eugene’s Library, quoted by Toland and La Monnoy, and gives their citations, at the same time observing that the piece is a Mahometan imposture. From another MS. belonging to Dr. Monkhouse, the Rev. Joseph White, in the notes to his Bampton Lectures, produces a long extract. Sale, who in his translation of the Koran, notices this Gospel, likewise had a MS. of it, which after his death was purchased by the Rev. Edm. Calamy, who permitted a copy to be taken by Mr. John Nickolls, the portrait collector: on his decease it became the property of Mr. Joseph Ames, author of the History of Printing, and is now in my possession.
The transcript was rediscovered in the 1970s in the University of Sydney‘s Fisher Library among the books of Charles Nicholson, labelled in English “Transcribed from ms. in possession of the Revd Mr Edm. Callamy who bought it at the decease of Mr George Sale … and now gave me at the decease of Mr John Nickolls, 1745; (signed) N. Hone”. The Sydney manuscript therefore is a copy of Sale’s own transcript; and has 130 pages but does not contain the entire text, as at the bottom of page 116 there is a note Cap 121 to 200 wanting, such that page 117 resumes with chapter 200 (in the Spanish numeration). Comparing the Sydney transcript with the counterpart passages quoted in Spanish by Sale, there are no substantial differences, but it would appear that sometime between Sale’s death in 1736 and 1745 some 80 chapters of his transcript had been lost; and are consequently also missing from the Sydney copy.
Fisher Library, University of Sydney. To the left of the image is Fisher North, and to the right is Fisher South.
The Spanish text is preceded by a note claiming that it was translated from Italian by Mustafa de Aranda, an Aragonese Muslim resident in Istanbul. A Morisco letter of around 1630, now in Madrid, confirms de Aranda as an associate of Ibrahim al-Taybili, in whose works is found the earliest reference to the Spanish Gospel. In the Spanish text, the translator’s note is itself preceded by a Preface by one assuming the pseudonym ‘Fra Marino’, claiming to have stolen a copy of the Italian version from the library of Pope Sixtus V. Fra Marino, clearly a high ranking Italian ecclesiastic, reports that having a post in the Inquisition Court, he had come into possession of several works which led him to believe that the Biblical text had been corrupted and that genuine apostolic texts had been improperly excluded. Fra Marino also claims to have been alerted to the existence of the Gospel of Barnabas, from an allusion in a work by Irenaeus against Paul; in a book which had been presented to him by a lady of the Colonna family. Marino outside Rome was a Colonna estate, and during the later 16th century Cardinal Ascanio Colonna, a close associate of both Sixtus V and Philip II of Spain, was building a palazzo there. 
The linguistic forms, spelling and punctuation of the Spanish text (as recorded in the Sydney transcript) are generally close to standard Castilian of the late 16th century; and lack the idiosyncrasies of the Italian manuscript. Hence, linguistically, the surviving Spanish text appears later than the surviving Italian text; but this does not necessarily confirm that the underlying Spanish text is secondary.