Deuteronomy 3:18-20

18“Then I commanded you [Reuben, Gad, and the half-tribe of Manasseh] at that time, saying, ‘The Lord your God has given you this land to possess; all you who are brave men shall cross over [the Jordan] armed before your brothers, the sons of Israel.

19But your wives and your children and your cattle—I know that you have much livestock—shall remain in your cities which I have given you,

20until the Lord gives rest to your fellow countrymen as [He has] to you, and they also possess the land which the Lord your God has given them beyond the Jordan. Then each of you may return to the land (possession) which I have given to you.’