I Kings 18:20-39.
In this week's haftorah, Elijah the Prophet demonstrates the worthlessness of the Baal, just as Moses chastised the Israelites for serving the Golden Calf, as discussed in this week's Torah reading.
The background of this week's haftorah: King Ahab and Queen Jezebel ruled the Northern Kingdom of Israel, and encouraged the worship of the Baal deity as well as other forms of idolatry. To prove that G‑d alone is in control and provides sustenance, Elijah decreed a drought on the kingdom--no rain fell for three years. When Ahab then accused Elijah of causing hardship for the Israelites, Elijah challenged him to a showdown. He, Elijah, would represent the cause of monotheism, and 850 idolatrous "prophets" would represent their cause. Ahab accepted.
The haftorah begins with Elijah, the Baal prophets, and many spectators gathering atop Mount Carmel. Elijah rebuked the people of Israel, uttering the famous words: "How long will you hop between two ideas? If the L-rd is G‑d, go after Him, and if the Baal, go after him."
Elijah then stated his challenge: "Give us two bulls and let them [the Baal prophets] choose one bull for themselves and cut it up and place it on the wood, but fire they shall not put; and I will prepare one bull, and I will put it on the wood, and fire will I not place. And you will call in the name of your deity, and I will call in the name of the L-rd, and it will be the G‑d that will answer with fire, he is G‑d."
The people agreed to the challenge, and the prophets of the Baal were first. The prophets' entreaties to their god went unanswered. Elijah taunted them: "Call with a loud voice, for you presume that he is a god. [Perhaps] he is talking or he is pursuing [enemies], or maybe he is on a journey; perhaps he is sleeping and will awaken..."
As evening approached, Elijah took center-stage. He built an altar, laid his offering upon it and surrounded it with water. "Lord, the G‑d of Abraham, Isaac and Israel," he declared. "Today let it be known that You are G‑d in Israel and that I am Your servant, and at Your word have I done all these things. Answer me, O L-rd, answer me, and this people shall know that You are the L-rd G‑d..."
A fire immediately descended from heaven and consumed the offering, as well as the altar and the surrounding water. "And all the people saw and fell on their faces, and they said, "The Lord is G‑d, the L-rd is G‑d."