After Elisha had instructed the young prophet to annoint Jehu as king of Israel,Jehu is also instructed to go & avenge the blood of the prophets & Lord's servants who had been killed by Jezebel.
2 Kings 9:6-8 (KJV)
6 And he arose, and went into the house; and he poured the oil on his head, and said unto him, Thus saith the LORD God of Israel, I have anointed thee king over the people of the LORD, even over Israel. 7 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. 8 For the whole house of Ahab shall perish: and I will cut off from Ahab him that pisseth against the wall, and him that is shut up and left in Israel:
But later in the book of Hosea God announces that he will punish the house of Jehu for the bloodshed at Jezreel.
Hosea 1:4 (KJV)
4 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.
It seems Jehu had carried out the instruction as given by the prophet
2 Kings 10:10-11 (KJV)
10 Know now that there shall fall unto the earth nothing of the word of the LORD, which the LORD spake concerning the house of Ahab: for the LORD hath done that which he spake by his servant Elijah. 11 So Jehu slew all that remained of the house of Ahab in Jezreel, and all his great men, and his kinsfolks, and his priests, until he left him none remaining.
So why was his house to be punished for the bloodshed at Jezreel?