II Chronicles 20:1, 23

It happened after this that the people of Moab with the people of Ammon, and others with them besides the Ammonites, came to battle against Jehoshaphat.

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.