2 Chronicles 20:22-23

22As they began to sing and praise, the LORD set ambushes against the men of Ammon and Moab and Mount Seir who were invading Judah, and they were defeated.

23The Ammonites and Moabites rose up against the men from Mount Seir to destroy and annihilate them. After they finished slaughtering the men from Seir, they helped to destroy one another.