Deuteronomy 3:16-17

16As for the tribes of Reuben and Gad, I gave them land from Gilead to the Arnon valley. The middle of the valley was the border of their land. Their land went as far as the Jabbok valley, which is the border of the Ammonites' land.

17The valley of the Jordan River was also a border of their land. It went from Lake Galilee as far as the Salt Sea, with Mount Pisgah to the east.