Both Jewish sources and Muslim sources seem to take for granted that at least some Arabs and/or Muslims are somehow descended from Abraham's son Ishmael (whether biologically or spiritually). See, for example, Mishneh Torah end of Hilchot Melakhim 11; Sefer HaIkkarim 4:42; Mefarshim to Genesis 37:27-28 and 39:1, etc. Though apparently there are traditions that some Arabs were descended from Yoktan/Joktan. https://en.wikipedia.org/wiki/Qahtanite. Apparently some Arab authors record this tradition pre-Islam. https://en.wikipedia.org/wiki/Ishmael#Pre-Islamic_Arabia
How old is this identification really? What are the earliest Jewish sources to support that identification? Does it match up with any evidence contemporary to the Bible in the way that, for example, archeological sources show who Moab, Babylon, and the Hittites were? If it's a later tradition, are there good theories about who made the identification and why? Basically, I'm wondering whether someone contemporary to the Torah would have clearly understood Ishmael as an origin story of the Arabs or if that arose later, and if the latter, when and why.