Albert Barnes Commentary 1 Kings 2:35

"And the king put Benaiah the son of Jehoiada in his room over the host; and Zadok the priest did the king put in the room of Abiathar." — 1 Kings 2:35 (ASV)

The high priesthood had, for some time, been divided in a certain sense between Zadok and Abiathar (see the note on 1 Kings 1:8). From that time on, Zadok became the sole high priest.