II Kings - Chapter 3
Looks Like Blood From Here
Ahab's son Yehoram became king of Israel after his brother Achaziah died and, like their parents, he was pretty rotten, just not as bad. He got rid of the altar to Baal that his father had made, although he left the asheira tree cult alone. Mesha, king of Moav, had paid Ahab a hefty annual tribute of sheep and rams. When Ahab died, Mesha stopped making payments, so Yehoram went out to battle Moav. He asked Yehoshafat, king of Judah, to join him and Yehoshafat agreed. (Edom was a vassal state to Judah, so they were on board, as well.) They went to Moav by way of the desert of Edom. En route, they ran out of water. Yehoram expressed the concern that G-d was handing Israel, Judah and Edom over to Moav. Yehoshafat asked if there was a prophet close enough to consult. There was: Elisha.
When the three rulers arrived, Elisha asked Yehoram, "What do we have to do with one another? Go ask your father's prophets (of Baal) or your mother's prophets (of the asheira cult)!" Yehoram replied, "Don't be like that! G-d is delivering us into Moav's hands!"
Elisha said, "I wouldn't help you, except that Yehoshafat is with you and he's a respectable person." A prophet needs to be in a good mood to receive a prophecy and seeing Yehoram got Elisha all upset, so he sent for a musician to calm him down.
Elisha prophesied, "You won't see rain, but the valley will be filled with water and all your animals will drink. More importantly, G-d will deliver Moav into your hands. You are to strike down every city, cut down every tree (normally forbidden in warfare), stop up the streams and fill the fields with rocks." The next morning, water was flowing in from the direction of Edom and it filled the land.
The army of Moav had prepared for the invasion and were standing ready. When they saw the sun shining on the water, it looked red to them, like blood. They assumed that the three invading armies must have turned on one another and wiped themselves out. They went to loot the scene of the massacre and found themselves in the middle of the Israelite camp, surrounded by sword-wielding Israelites. The Israelites easily defeated them, then did all that Elisha had commanded them.
The king of Moav saw he was defeated. He tried to break through to attack the king of Edom, but he was unable. He then sacrificed his son. (It's unclear to whom "his" refers here. Rashi says it means the king of Moav sacrificed his own son, but Radak says it means the king of Edom's son.) The human sacrifice angered G-d and caused Him to recall the idolatry that was going on in Israel. G-d's favor removed, the siege was discontinued.