Numbers 32:28-30

28So Moses gave orders about them to Eleazar the priest, to Joshua son of Nun, and to the heads of the families of the Israelite tribes.

29Moses said to them: “If the Gadites and the Reubenites cross the Jordan with you, each one equipped for battle in the Lord’s presence, and you conquer the land, then you must allot them the territory of Gilead as their possession.

30But if they do not cross over with you armed, they must receive possessions among you in Canaan.”