the Spirit of the LORD came upon one of the men standing there. His name was Jahaziel son of Zechariah, son of Benaiah, son of Jeiel, son of Mattaniah, a Levite who was a descendant of Asaph.
He said, "Listen, King Jehoshaphat! Listen, all you people of Judah and Jerusalem! This is what the LORD says: Do not be afraid! Don't be discouraged by this mighty army, for the battle is not yours, but God's.
Tomorrow, march out against them. You will find them coming up through the ascent of Ziz at the end of the valley that opens into the wilderness of Jeruel.
But you will not even need to fight. Take your positions; then stand still and watch the LORD's victory. He is with you, O people of Judah and Jerusalem. Do not be afraid or discouraged. Go out there tomorrow, for the LORD is with you!"
Then King Jehoshaphat bowed down with his face to the ground. And all the people of Judah and Jerusalem did the same, worshiping the LORD.
Then the Levites from the clans of Kohath and Korah stood to praise the LORD, the God of Israel, with a very loud shout.
Early the next morning the army of Judah went out into the wilderness of Tekoa. On the way Jehoshaphat stopped and said, "Listen to me, all you people of Judah and Jerusalem! Believe in the LORD your God, and you will be able to stand firm. Believe in his prophets, and you will succeed."
After consulting the leaders of the people, the king appointed singers to walk ahead of the army, singing to the LORD and praising him for his holy splendor. This is what they sang: "Give thanks to the LORD; his faithful love endures forever!"
At the moment they began to sing and give praise, the LORD caused the armies of Ammon, Moab, and Mount Seir to start fighting among themselves.
The armies of Moab and Ammon turned against their allies from Mount Seir and killed every one of them. After they had finished off the army of Seir, they turned on each other.
So when the army of Judah arrived at the lookout point in the wilderness, there were dead bodies lying on the ground for as far as they could see. Not a single one of the enemy had escaped.
King Jehoshaphat and his men went out to gather the plunder. They found vast amounts of equipment, clothing, and other valuables -- more than they could carry. There was so much plunder that it took them three days just to collect it all!
References for 2 Chronicles 20:25