Deuteronomy 3:18-22 - Instructions To The Transjordanian Tribes
18 And I commanded you the same time, ye Reuben and Gad, saying, 'The LORD your God hath given you this land to enjoy it: see that ye go harnessed before your brethren the children of Israel, all that are men of war among you. 19 Your wives only, your children and your cattle - for I know that ye have much cattle - shall abide in your cities which I have given you, 20 until the LORD have given rest unto your brethren as well as unto you, and until they also have conquered the land which the LORD your God hath given them beyond Jordan: and then return again every man unto his possession which I have given you.'
21 And I warned Joshua the same time, saying, 'Thine eyes have seen all that the LORD your God hath done unto these two kings; even so the LORD will do unto all kingdoms whither thou goest. 22 Fear them not, for the LORD your God, he it is that fighteth for you.'