Deuteronomy 3:18-20

18I gave the tribes of Reuben and Gad and half of the tribe of Manasseh this command: “The Lord your God has given you this land so that you can take possession of it. All your soldiers must be ready for battle when they cross ⌞the Jordan River⌟ ahead of the other Israelites.

19I know you have a lot of livestock. Your wives, children, and livestock must stay here in the cities that I gave you.

20Your soldiers will go with the other Israelites until they take possession of the land the Lord your God is giving them on the other side of the Jordan River. Then they will have a place to rest as you have. After that each of you may go back to the land I gave you.”