We do not “know” that the beloved disciple is John, but a common sense reading of the book, combined with the tradition that it was John himself who wrote the gospel makes John by far the most likely candidate. Besides we can combine this with what we know of John from the other gospels, plus what we know about him from church history. Putting all this together makes it pretty much a slam dunk that the apostle John was the beloved disciple. I have seen other proposals and they seem to me to be extremely unlikely. But…. I would not bet my life or my faith on assuming that the beloved disciple was John. My faith does not depend on this. The author of the book does not name himself, yet he does name many of the apostles, including all the apostles who play a prominent role in the synoptic gospels. The exception, is John. John is not named in the book of John, yet we have this mysterious apostle known as the beloved disciple. The only reasonable conclusion is that he is John. I have heard no other believable explanation. So, for now, I am assuming it is John.
Anyone who claims that Islam came before Christianity had better go back to the history books. There is no debate–none–that this religion was founded by Muhammad, who lived from AD 571-632. How could a man who lived in the sixth and seventh centuries found a religion almost six hundred years before he lived? Like I already said, all agree, including Muslims, that the religion known as Islam was founded by Muhammad. He started with literally zero believers. The religion of Islam outside of Muhammad and the Qur’an is not a religion at all.
Now, it is true that Muhammad claimed Abraham took a pilgrimage to Mecca with Ishmael. There is no historical evidence for the truth of this. If anyone would know whether this happened, it would be the Jews, not Muhammad!! Nevertheless, even if we can accept as truth that Abraham traveled to Mecca with Ismael, this still would not change the historical fact that Muhammad founded the religion we know of as Islam. Saying that Islam existed before Muhammad would be like saying that Christianity existed before Jesus Christ lived. What would that even mean? Ishmael may be Arab, and the Arabs may be descended from Ishmael, but Ishmael was not Muslim. It was quite literally impossible for Ishmael to be a Muslim.
It is true that Muslims claim that Jesus was not actually killed on the cross, but your argument is spot-on. Who are going to believe–his own mother and his best friend John or are we going to believe a man who lived six hundred years later, who never met Jesus, who makes up a story, not because of evidence, but because his religion is not consistent with a prophet who is killed on a cross. The idea that Muhammad would be right and the eye-witnesses would be wrong is ludicrous and does not even deserve serious consideration, yet this is a central tenet of Islam. Your Muslim friend may be happy (under a false premise) that Jesus did not die, but if Jesus was not killed and raised from the dead, then you and I are still in our sins. I am not “happy” that Jesus was tortured to death, but I am thankful that he did this for me.
This explains why Muslims go to such great lengths to try to prove that the Bible is “corrupt.” Anyone with plain common sense knows that the eye witnesses are more meaningful that Muhammad on the events of the first century. Besides, the Qur’an itself calls the New Testament “injil” which means the word of God. The only possible path forward is to claim that the very accounts of the crucifixion are a later invention of the church. The problem is that even Roman and Jewish sources agree that the Romans killed Jesus of Nazareth, and we have manuscripts from the second century. For this reason, the Qur’an is completely discredited, at least as being inspired by God.