WHAT IS THE BOOK OF THE WARS OF THE LORD?

Numbers 21:14-15 says, "

That is why the Book of the Wars of the Lord says:

“. . . Zahab[a] in Suphah and the ravines,
the Arnon 15 and[b] the slopes of the ravines
that lead to the settlement of Ar
and lie along the border of Moab.”

The Book of the Wars of the Lord (סֵפֶר מִלְחֲמֹת יהוה) is one of several non-canonical books referenced in the Bible which have now been completely lost. ... The Book of the Wars of the LORD is cited in the medieval Book of Jasher as being a collaborative record written by Moses, Joshua, and the children of Israel.

Exodus: Gods and Kings