Numbers 32:20-22

20Moses replied to them, “If you do this — if you arm yourselves for battle before the Lord,

21and every one of your armed men crosses the Jordan before the Lord until he has driven his enemies from his presence,

22and the land is subdued before the Lord  — afterward you may return and be free from obligation to the Lord and to Israel. And this land will belong to you as a possession before the Lord.