Deuteronomy 3:12, 16

“And this land, which we possessed at that time, from Aroer, which is by the River Arnon, and half the mountains of Gilead and its cities, I gave to the Reubenites and the Gadites.

And to the Reubenites and the Gadites I gave from Gilead as far as the River Arnon, the middle of the river as the border, as far as the River Jabbok, the border of the people of Ammon