Deuteronomy 2:24

2:24 Get up, make your way across Wadi Arnon. Look! I have already delivered over to you Sihon the Amorite, king of Heshbon, and his land. Go ahead! Take it! Engage him in war!

Deuteronomy 3:16

3:16 To the Reubenites and Gadites I allocated the territory extending from Gilead as far as Wadi Arnon (the exact middle of the wadi was a boundary) all the way to the Wadi Jabbok, the Ammonite border.