Numbers 32:29-31

The Voice

Moses: ²⁹ If indeed the Gadites and Reubenites fight in front of the Eternal One and beside the rest of you to successfully dominate that land across the Jordan River, then you must honor their desire to return here to have this Gilead land for their own. ³⁰ But if they don’t take up their weapons and go with you into battle, then their ownership of this territory is null and void, and they shall be assigned land in Canaan along with the rest of the Israelite tribes.

Reubenites and Gadites: ³¹ Exactly as we understand this to be the will of God, we will do it.