2 Chronicles 20:20-23

¶ And they rose early in the morning, and went forth into the wilderness of Tekoa: and as they went forth, Jehoshaphat stood and said, Hear me, O Judah, and ye inhabitants of Jerusalem; Believe in the LORD your God, so shall ye be established; believe his prophets, so shall ye prosper.

And when he had consulted with the people, he appointed singers unto the LORD, and that should praise the beauty of holiness, as they went out before the army, and to say, Praise the LORD; for his mercy [endureth] for ever.

And when they began to sing and to praise, the LORD set ambushments against the children of Ammon, Moab, and mount Seir, which were come against Judah; and they were smitten.

For the children of Ammon and Moab stood up against the inhabitants of mount Seir, utterly to slay and destroy [them]: and when they had made an end of the inhabitants of Seir, every one helped to destroy another.