Numbers 21:13-15

From there they went on and put up their tents on the other side of the Arnon, which is on the waste land at the edge of the land of the Amorites; for the Arnon is the line of division between Moab and the Amorites: As it says in the book of the Wars of the Lord, Vaheb in Suphah, and the valley of the Amon; The slope of the valleys going down to the tents of Ar and touching the edge of Moab.