II Chronicles - Chapter 20
Edomites in the Midst
The nations of Moab and Ammon attacked Judah, with the help of some Edomites. Yehoshafat was informed and he declared a fast day on which the nation should pray to G-d. The king stood among the people at the Temple and prayed, saying that G-d is over all the nations and that no one can withstand His might. Now His faithful are being attacked by two nations that had antagonized them when they left Egypt. At that time, G-d did not permit the Jews to invade these nations, but they couldn't leave well enough alone. Since the approaching army has them outmatched, won't G-d please take care of things?
A Levite named Yachaziel received a prophecy from G-d. He said that the people should not be worried, as this was G-d's fight, not theirs. They should go to meet the invaders and watch what happens. Yehoshafat and the people all bowed down on the ground before G-d and the Levites sang praises.
The next day, they went out to the battle site. Yehoshafat spoke words of encouragement to them and appointed Levites to sing Psalms to G-d. When they broke out in song, G-d struck the enemy army. Confused as to the source of the attack, the forces of Ammon and Moab turned on the Edomites in their midst. When they had destroyed them, they turned on one another until they wiped themselves out. The people of Judah witnessed this amazing spectacle, then helped themselves to the spoils. There was so much booty, it took three days to gather it all up. On the fourth day, they gathered to praise G-d in a place they named "Emek Bracha" ("valley of blessing"), then they returned to Jerusalem.
They returned home playing instruments and singing songs of praise to G-d. Other nations were suitably intimidated when they heard about this incident, so the rest of Yehoshafat's reign was pretty quiet.
Yehoshafat ruled for 25 years and he was righteous, as his father Asa had been, though he also did not remove the private altars to G-d. Yehoshafat partnered with Ahab's son and successor, Achazya, to build ships to travel to Tarshish. A prophet named Eliezer told Yehoshafat that he would not succeed, since he had joined forces with an evil man. Sure enough, the ships were unable to successfully complete the voyage.