Since Ahab humbled himself before him, God decided to punish his son instead.
He [Ahab] rent his clothes, and put sackcloth upon his flesh, and fasted, and lay in sackcloth, and went softly. And the word of the LORD came to Elijah the Tishbite, saying, Seest thou how Ahab humbleth himself before me? because he humbleth himself before me, I will not bring the evil in his days: but in his son's days will I bring the evil upon his house. 1 Kings 21:27-29
God killed Ahab for showing mercy to king Benhadad.
Thus saith the LORD, Because thou hast let go out of thy hand a man whom I appointed to utter destruction, therefore thy life shall go for his life, and thy people for his people. 1 Kings 20:42
And the dogs licked his blood, as God told Ahab they would do.
Thus saith the LORD, Hast thou killed, and also taken possession? And thou shalt speak unto him, saying, Thus saith the LORD, In the place where dogs licked the blood of Naboth shall dogs lick thy blood, even thine. 1 Kings 21:19
God put lying spirits in the mouths of his prophets so they would give Ahab bad advice that would get him killed.
And the LORD said, Who shall persuade Ahab, that he may go up and fall at Ramothgilead? ... And there came forth a spirit, and stood before the LORD, and said, I will persuade him. 1 Kings 22:20-21
Now therefore, behold, the LORD hath put a lying spirit in the mouth of all these thy prophets. 1 Kings 22:23
And the king ... died at even: and the blood ran out of the wound into the midst of the chariot ... and the dogs licked up his blood; and they washed his armour; according unto the word of the LORD. 1 Kings 22:35-38
