2 Chronicles (Author Compiled by Isaiah and Ezra from records of Nathan, Gad, Iddo, Ahijah, Jehu and others.)
20:21And 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.
Original from The Bible Foundation - bf.org. They claim public domain status for their original text.