Numbers 21:13-15

Then they moved out and camped on the far side of the Arnon River, in the wilderness adjacent to the territory of the Amorites. The Arnon is the boundary line between the Moabites and the Amorites. For this reason The Book of the Wars of the LORD speaks of “the town of Waheb in the area of Suphah, and the ravines of the Arnon River, and the ravines that extend as far as the settlement of Ar on the border of Moab.”