21 So she said, "Let Abishag the Shunammite be given to Adonijah your brother as wife." 22 And King Solomon answered and said to his mother, "Now why do you ask Abishag the Shunammite for Adonijah? Ask for him the kingdom also--for he is my older brother--for him, and for Abiathar the priest, and for Joab the son of Zeruiah." 23 Then King Solomon swore by the Lord, saying, "May God do so to me, and more also, if Adonijah has not spoken this word against his own life! 24 Now therefore, as the Lord lives, who has confirmed me and set me on the throne of David my father, and who has established a house [1] for me, as He promised, Adonijah shall be put to death today!" 25 So King Solomon sent by the hand of Benaiah the son of Jehoiada; and he struck him down, and he died.
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.