2 Chronicles 20:10, 23

Now behold, the sons of Ammon and Moab and Mount Seir, whom You would not allow Israel to invade when they came from the land of Egypt (for they turned away from them and did not destroy them), [Deut 2:9]

For the sons of Ammon and Moab [suspecting betrayal] rose up against the inhabitants of Mount Seir, completely destroying them; and when they had finished with the inhabitants of Seir, they helped to destroy one another.