Solomon was told, “Look, Adonijah fears you; see, he has taken hold of the horns of the altar, saying, ‘May King Solomon solemnly promise me today that he will not kill his servant with the sword.’”
When the news reached Joab (for Joab had supported Adonijah, although he had not supported Absalom), he ran to the tent of the Lord and grabbed hold of the horns of the altar.
Aaron is to make atonement on its horns once in the year with some of the blood of the sin offering for atonement; once in the year he is to make atonement on it throughout your generations. It is most holy to the Lord.”