Numbers 21:13-15

13Then they left there and they put up their tents on the north side of the River Arnon. The River Arnon is the border between the Moabites and the Amorites.

14You can read about this in the Book of the Lord's Wars. It talks about Waheb in Suphah and about the valleys of the River Arnon.

15It also speaks about the sides of the valleys on the border of Moab that lead to the town of Ar.