Numbers 32:29-33
29 Moses said to them, “If the sons of Gad and the sons of Reuben will cross over the Jordan with you, every man armed for battle before the Lord, and the land is subdued before you, then you shall give them the land of Gilead [east of the Jordan River] as a possession;
30 but if they will not cross over with you armed, they shall have possessions among you in the land of Canaan [and surrender their right to their land east of the Jordan River].”
31 The sons of Gad and the sons of Reuben answered, “As the Lord has said to your servants, so will we do.
32 We will cross over armed before the Lord into the land of Canaan, so that the possession of our inheritance on [the east] side of the Jordan may be ours.”