Numbers 32:20-29

Then Moses said to them, “If you will do this—if you will arm yourselves before the LORD for battle and if all of you who are armed cross over the Jordan before the LORD until he has driven his enemies out before him— then when the land is subdued before the LORD, you may return and be free from your obligation to the LORD and to Israel. And this land will be your possession before the LORD. “But if you fail to do this, you will be sinning against the LORD; and you may be sure that your sin will find you out. Build cities for your women and children, and pens for your flocks, but do what you have promised.” The Gadites and Reubenites said to Moses, “We your servants will do as our lord commands. Our children and wives, our flocks and herds will remain here in the cities of Gilead. But your servants, every man who is armed for battle, will cross over to fight before the LORD, just as our lord says.” Then Moses gave orders about them to Eleazar the priest and Joshua son of Nun and to the family heads of the Israelite tribes. He said to them, “If the Gadites and Reubenites, every man armed for battle, cross over the Jordan with you before the LORD, then when the land is subdued before you, you must give them the land of Gilead as their possession.