2 Chronicles 20:10, 23

Now behold, the sons of Ammon and Moab and Mount Seir, whom You did not let Israel invade when they came out of the land of Egypt (they turned aside from them and did not destroy them)

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