Thus saith the Lord God of Israel, I have anointed thee king over the people of the Lord, even over Israel. And thou shalt smite the house of Ahab thy master, that I may avenge the blood of my servants the prophets, and the blood of all the servants of the Lord, at the hand of Jezebel. For the whole house of Ahab shall perish: and I will cut off from Ahab him that pisseth against the wall. 2 Kings 9:6-8God praised Jehu after the massacres saying he had "done well in executing that which is right in mine eyes."
And the LORD said unto Jehu, Because thou hast done well in executing that which is right in mine eyes, and hast done unto the house of Ahab according to all that was in mine heart, thy children of the fourth generation shall sit on the throne of Israel. 2 Kings 10:30
The destruction of Ahaziah was of God by coming to Joram: for when he was come, he went out with Jehoram against Jehu the son of Nimshi, whom the LORD had anointed to cut off the house of Ahab. And it came to pass, that, when Jehu was executing judgment upon the house of Ahab, and found the princes of Judah, and the sons of the brethren of Ahaziah, that ministered to Ahaziah, he slew them. 2 Chronicles 22:7
And the LORD said unto him, Call his name Jezreel; for yet a little while, and I will avenge the blood of Jezreel upon the house of Jehu, and will cause to cease the kingdom of the house of Israel. Hosea 1:4