Numbers 21:13-15

From thence they removed, and pitched on the other side of Arnon, which is in the wilderness that cometh out of the coasts of the Amorites: for Arnon is the border of Moab, between Moab and the Amorites. Wherefore it is said in the book of the wars of the LORD, What he did in the Red sea, And in the brooks of Arnon, And at the stream of the brooks That goeth down to the dwelling of Ar, And lieth upon the border of Moab.