2 Chronicles (Author Compiled by Isaiah and Ezra from records of Nathan, Gad, Iddo, Ahijah, Jehu and others.)
Chapter 20
15and he said, Be attentive, all Judah, and ye inhabitants of Jerusalem, and thou king Jehoshaphat! Thus saith Jehovah unto you: Fear not, nor be dismayed by reason of this great multitude; for the battle is not yours, but God's.
Original from The Bible Foundation - bf.org. They claim public domain status for their original text.