Numbers 32:31-33

31The men in the tribes of Reuben and Gad said, ‘We will do what the Lord has told us to do.

32We will take our weapons and we will cross over the Jordan River to fight on behalf of the Lord in Canaan. But then we will live in our land here on this side of the river.’

33So Moses gave to them all the kingdom of Sihon, king of the Amorites and Og, the king of Bashan. He gave to them the land with its towns and all the land round the towns. He gave it to the descendants of Gad and of Reuben and half of the tribe of Joseph's son Manasseh.