Numbers 32:29-33

And Moses said to them, “If the sons of Gad and the sons of Reuben, everyone who is armed for battle, cross with you over the Jordan in the presence of the Lord, and the land is subdued before you, then you shall give them the land of Gilead as their property;

but if they do not cross over with you armed, they shall instead be settled among you in the land of Canaan.”

And the sons of Gad and the sons of Reuben answered, saying, “As the Lord has said to your servants, so we will do.

We ourselves will cross over armed in the presence of the Lord into the land of Canaan, and the property of our inheritance shall remain with us across the Jordan.”

So Moses gave to them, to the sons of Gad, the sons of Reuben, and to the half-tribe of Joseph’s son Manasseh, the kingdom of Sihon, king of the Amorites and the kingdom of Og, the king of Bashan, the land with its cities with their territories, the cities of the surrounding land.