21 "Then let your brother Adonijah marry Abishag, the girl from Shunem," she replied. 22 "How can you possibly ask me to give Abishag to Adonijah?" King Solomon demanded. "You might as well ask me to give him the kingdom! You know that he is my older brother, and that he has Abiathar the priest and Joab son of Zeruiah on his side." 23 Then King Solomon made a vow before the Lord : "May God strike me and even kill me if Adonijah has not sealed his fate with this request. 24 The Lord has confirmed me and placed me on the throne of my father, David; he has established my dynasty as he promised. So as surely as the Lord lives, Adonijah will die this very day!" 25 So King Solomon ordered Benaiah son of Jehoiada to execute him, and Adonijah was put to death.
Matthew Henry's Commentary on 1 Kings 2:21-25
Commentary on 1 Kings 2:12-25
(Read 1 Kings 2:12-25)
Solomon received Bathsheba with all the respect that was owing to a mother; but let none be asked for that which they ought not to grant. It ill becomes a good man to prefer a bad request, or to appear in a bad cause. According to eastern customs it was plain that Adonijah sought to be king, by his asking for Abishag as his wife, and Solomon could not be safe while he lived. Ambitious, turbulent spirits commonly prepare death for themselves. Many a head has been lost by catching at a crown.