Numbers 21:13-14

Brenton(i) 13 And they departed thence and encamped on the other side of Arnon in the wilderness, the country which extends from the coasts of the Amorites; for Arnon is the borders of Moab, between Moab and the Amorites. 14 Therefore it is said in a book, A war of the Lord has set on fire Zoob, and the brooks of Arnon.