Numbers 21:13, 24

From there they moved and camped on the other side of the Arnon, which is in the wilderness that extends from the border of the Amorites; for the Arnon is the border of Moab, between Moab and the Amorites.

Then Israel defeated him with the edge of the sword, and took possession of his land from the Arnon to the Jabbok, as far as the people of Ammon; for the border of the people of Ammon was fortified.