2 Chronicles 20:22-23

22And when they began the song of triumph and praise, Jehovah set liers-in-wait against the children of Ammon, Moab, and mount Seir, who had come against Judah, and they were smitten.

23And the children of Ammon and Moab stood up against the inhabitants of mount Seir, to exterminate and destroy [them]; and when they had made an end of the inhabitants of Seir, they helped to destroy one another.