II Chronicles 20:10, 23

And now, here are the people of Ammon, Moab, and Mount Seir—whom You would not let Israel invade when they came out of the land of Egypt, but they turned from them and did not destroy them

For the people of Ammon and Moab stood up against the inhabitants of Mount Seir to utterly kill and destroy them. And when they had made an end of the inhabitants of Seir, they helped to destroy one another.