Numbers 32:20-27

20Moses replied, “If you will do as you say, if you will arm yourselves before the Lord for war,

21and every armed man of yours will cross the Jordan before the Lord until He has driven out His enemies before Him,

22and the land [west of the Jordan] is subdued before the Lord, then afterward you shall return and be blameless [in this matter] before the Lord and before Israel, and this land [east of the Jordan] shall be yours as a possession before the Lord.

23But if you do not do this, behold, you will have sinned against the Lord; and be sure that your sin will find you out.

24Build yourselves cities for your children, and folds for your sheep, and do that of which you have spoken.”

25Then the descendants of Gad and of Reuben said to Moses, “Your servants will do just as my lord commands.

26Our children, our wives, our livestock, and all our cattle shall be there in the cities of Gilead.

27But your servants will cross over, every man armed for war, before the Lord to the battle, just as my lord says.”