Who told Benaiah to kill Joab?
Solomon
So Benaiah the son of Jehoiada went up, and fell upon him, and slew him: 1 Kings 2:31-34
1 Kings 2:31And the king said unto him, Do as he hath said, and fall upon him, and bury him; that thou mayest take away the innocent blood,
which Joab shed, from me, and from the house of my father. ...
1 Kings 2:31