1 Kings 2:22-23

22King Solomon answered his mother, "And why do you ask Abishag the Shunammite for Adonijah? Ask for him the kingdom also, for he is my older brother, and on his side are Abiathar the priest and Joab the son of Zeruiah."

23Then King Solomon swore by the Lord, saying, "God do so to me and more also if this word does not cost Adonijah his life!