I Kings - Chapter 18
Hashem Hu Ha'Elokim! Hashem Hu Ha'Elokim!
This chapter tells of one of the most significant events in Jewish history: the "showdown" between G-d and the Baal on Mt. Carmel. (It wasn't much of a showdown since one of the parties - the Baal - never actually showed up. But that's because he doesn't exist.)
Let's start at the beginning:
The drought lasted three years and G-d told Elijah to go to Ahab and end it. The head of Ahab's household was the righteous Obadaiah, a convert from Edom (see Sanhedrin 39b). When Jezebel was wiping out all the prophets, Obadaiah hid 100 of them in caves and supported them with his own money. As a reward, he became a prophet, one of the twelve "minor prophets" whose books make up the volume called Trei Asar. Elijah approached Obadiah and said, "Tell Ahab that I'm here." Obadiah balked. "Oh, no. Ahab has been looking for you everywhere. I'm going to go get him, G-d will whisk you away to safety, and Ahab will kill me." Elijah replied, "Don't worry, I'll still be here when you get back." So Obadiah went and got Ahab.
When Ahab saw Elijah, he blamed the prophet for causing the drought. Elijah replied, "It's not my fault, it's yours." He told Ahab to get the 450 prophets of Baal as well as the 400 prophets of the asheira tree worshippers.
Elijah, the people, and the prophets of Baal gathered on Mt. Carmel. (The asheira prophets were no shows.) Elijah said, "Either G-d is the L-rd or Baal is - it's time to pick one!" He proposed the following contest. There were two bulls. The Baal worshippers would prepare one and he would prepare the other. Whichever one would be consumed by a fire from Heaven must be an offering to the one true Ruler. Everyone thought this was a good idea and the priests of Baal got to go first. They prepared their sacrifice and prayed, danced and cut themselves for hours, but there was no reply, because nobody was listening. Elijah mocked them. "Shout louder! Maybe Baal is sleeping, or perhaps he's in the bathroom!" Eventually the prophets of Baal had to give up.
Then it was Elijah's turn. He had a huge trench dug around his altar. He then had water poured over his sacrifice until it filled the trench. (Keep in mind that this was during a drought and water was very precious!) A fire came down from G-d and consumed the sacrifice and licked up all the water in the trench. The people cried out "Hashem Hu Ha'Elokim! G-d is the L-rd!" (We say this seven times at the conclusion of the Yom Kippur service - this is where it comes from.) Elijah told the people to seize the prophets of Baal and the people executed them.
Fasting is a traditional way of praying for rain. Elijah told Ahab, "Go and eat because rain is coming." Elijah prayed and sent his attendant out to check the horizon for clouds. Nothing. He checked seven times; on the seventh, he saw a small cloud, like a man's fist. Elijah told Ahab to hit the road so the rain wouldn't affect his journey. The skies darkened and rain came down. Ahab headed for home and Elijah accompanied him, out of respect for the king.