Numbers 21:13-15

13They set out from there and camped on the other side of the Arnon River, in the wilderness that extends from the Amorite border, because the Arnon was the Moabite border between Moab and the Amorites.

14Therefore it is stated in the Book of the Lord’s Wars: Waheb in Suphah and the ravines of the Arnon,

15even the slopes of the ravines that extend to the site of Ar and lie along the border of Moab.