Numbers 21:13-15

13From thence they removed, and encamped on the other side of the Arnon, which is in the wilderness that comes out of the border of the Amorites. For the Arnon is the border of Moab, between Moab and the Amorites.

14Therefore it is said in the book of the wars of Jehovah, Vaheb in Suphah, and the brooks of Arnon;

15And the stream of the brooks which turneth to the dwelling of Ar, And inclineth toward the border of Moab.