1 Kings 2:23-25

23Then King Solomon made this strong promise in the Lord's name. He said, ‘Because Adonijah has asked to have Abishag as his wife, I will certainly punish him with death. If I do not do that, I pray that God will punish me instead!

24As surely as the Lord lives, Adonijah must die today. The Lord has done everything that he promised to me. He has made me strong so that now I rule on the throne of my father David. And my descendants will continue to rule as kings after me.’

25So King Solomon commanded Jehoiada's son Benaiah to kill Adonijah. So Adonijah died.