(Bamidbar 10:32) "And it shall be, if you go with us, that good which the L-rd will accord to us, we shall accord to you." Now what good did they accord to him? They said: When Israel apportioned the land, they left to him the choicest land of Jericho, five hundred by five hundred cubits. Whoever would build the Temple, would take that land, and (in the interim) it was given (as a holding) to the sons of Yithro, as it is written (I Kings 6:1) "And it was in the four hundred and eighteenth year of the exodus of the children of Israel from the land of Egypt" (that the Temple was built).
Deduct forty years for their journeying in the desert, and we find them (the sons of Yithro) to have eaten of that land for four hundred and forty years, and when the Shechinah reposed itself in the portion of Benjamin, the sons of Benjamin came to take their portion, and they (the sons of Yithro) vacated it for them.