The book of Jashar is one of the many books cited in the OT. Following is
a list (possibly incomplete) of sources cited in the O.T. books. The list
omits references to other O.T. books. These works are
“extrabiblical”-outside (extra, Latin) the Bible.

The Book of the Wars of the Lord-Numbers 21:14
The Poets-Numbers 21:27
The Book of the Annals of the Kings of Media and Persia-Esther 10:2
The Book of Jashar-Joshua 10:13, 2 Samuel 1:18
The Sayings of the Wise-Proverbs 22:17+
The Sayings of Agur-Proverbs 30
The Sayings of King Lemuel-Proverbs 31:1-9
The Book of the Annals of the Kings of Israel-1 Kings 14:19 etc.
The Book of the Annals of the Kings of Judah-1 Kings 14:29 etc.
The Book of the Kings of Judah and Israel-2 Chronicles 16:11
The Annotations of the Prophet Iddo-2 Chronicles 13:22
The Vision of the Prophet Isaiah-2 Chronicles 32:32
Genealogical records-Nehemiah 7, Ezra 2
The Book of the Annals of Solomon-1 Kings 11:41
The Book of the Annals of King David-1 Chronicles 27:24
The Records of Samuel the Seer-1 Chronicles 29:29
The Records of Nathan the Prophet-1 Chronicles 29:29
The Records of Gad the Seer-1 Chronicles 29:29
The Visions of Iddo the Seer-2 Chronicles 9:29
The Prophecy of Ahijah the Shilonite-2 Chronicles 9:29
The Annals of Jehu son of Hanani-2 Chronicles 20:34
The Letter of Elijah to Jehoram-2 Chronicles 21:12+
The Annotations of the Book of the Kings-2 Chronicles 24:27
The Laments of Jeremiah for Josiah-2 Chronicles 35:25

Note:
1. It is always possible that some of these sources may be identical to
other sources, although with a different name.
2. This is probably not a complete list.
3. This study makes it clear that the Bible frequently quotes sources,
without necessarily making those sources “inspired.”

Douglas Jacoby, from www.douglasjacoby.com