2 Kings 9:3
Then take the box of oil, and pour it on his head, and say, Thus saith the LORD, I have anointed thee king over Israel. Then open the door, and flee, and tarry not. Then take the box of oil, and pour it on his head, and say, Thus saith the LORD, I have anointed thee king over Israel. Then open the door, and flee, and tarry not.
Elisha in obedience to God's command sent a prophetic messenger to Ramoth Gilead to anoint Jehu king of Israel. The anointing took place while Israel and Judah were campaigning together against Syria at Ramoth Gilead. King Jehoram had been wounded in the fighting and had returned to Jezreel to recover. Jehu had been left in charge of the army in his absence.
The pouring of oil on his head declared Jehu's royal authority as king over Israel. That anointing began his divine commission to destroy the house of Ahab. It charged him to avenge the blood of the Lord's servants and prophets shed by Jezebel.