Numbers 32:30

27 But your servants will go over, every man armed for war, before the Lord to the fight, as my lord says.

28 So Moses gave orders about them to Eleazar the priest and to Joshua, the son of Nun, and to the heads of families of the tribes of the children of Israel.

29 And Moses said to them, If the children of Gad and the children of Reuben go with you over Jordan, every man armed for the fight before the Lord, and all the land is given into your hands, then let them have the land of Gilead for a heritage:

30 But if they do not go over with you armed, they will have to take their heritage with you in the land of Canaan.

31 Then the children of Gad and the children of Reuben said, As the Lord has said to your servants, so will we do.

32 We will go over armed before the Lord into the land of Canaan, and you will give us our heritage on this side of Jordan.

33 So Moses gave to them, even to the children of Gad and the children of Reuben and to the half-tribe of Manasseh, the son of Joseph, the kingdom of Sihon, king of the Amorites and Og, king of Bashan, all the land with its towns and the country round them.