Numbers 32:26-29

26Our children, our wives, our flocks, and all of our herds will remain here in the cities of Gilead.

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

28Moses then gave orders about them to Eleazar the kohen, Joshua son of Nun, and to the chiefs of the fathers of the tribes of Bnei-Yisrael.

29Moses said to them, “If the sons of Gad and Reuben cross over the Jordan with you, everyone armed for battle before Adonai, when the land is subdued before you, then give them the territory of Gilead as a possession.