21 She said, "Give Abishag the Shunammite to your brother Adonijah as his wife." 22 King Solomon answered his mother, "What kind of favor is this, asking that Abishag the Shunammite be given to Adonijah? Why don't you just ask me to hand over the whole kingdom to him on a platter since he is my older brother and has Abiathar the priest and Joab son of Zeruiah on his side!" 23 Then King Solomon swore under God, "May God do his worst to me if Adonijah doesn't pay for this with his life! 24 As surely as God lives, the God who has set me firmly on the throne of my father David and has put me in charge of the kingdom just as he promised, Adonijah will die for this - today!" 25 King Solomon dispatched Benaiah son of Jehoiada; he struck Adonijah 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.