Numbers 32:27

25The children of Gad and the children of Reuben spoke to Moses, saying, “Your servants will do as my lord commands.

26Our little ones, our wives, our flocks, and all our livestock shall be there in the cities of Gilead;

27but your servants will pass over, every man who is armed for war, before the LORD to battle, as my lord says.”

28So Moses commanded concerning them to Eleazar the priest, and to Joshua the son of Nun, and to the heads of the fathers’ households of the tribes of the children of Israel.

29Moses said to them, “If the children of Gad and the children of Reuben will pass with you over the Jordan, every man who is armed to battle before the LORD, and the land is subdued before you, then you shall give them the land of Gilead for a possession;