This Bible contradiction is from the Skeptic's Annotated Bible.
God commended him for it. (He told him to perform the killings.)
2 Kings 10:30 View context
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 Chronicles 22:7 View context
And 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.
God condemned him for it.
Hosea 1:4 View context
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.