1 Kings 2:23-25

1 Kings 2:23-25 King James Version (KJV)
23 Then king Solomon sware by the Lord, saying, God do so to me, and more also, if Adonijah have not spoken this word against his own life.
24 Now therefore, as the Lord liveth, which hath established me, and set me on the throne of David my father, and who hath made me an house, as he promised, Adonijah shall be put to death this day.
25 And king Solomon sent by the hand of Benaiah the son of Jehoiada; and he fell upon him that he died.
An American English Bible
With Old Testament based on the Greek Septuagint

23 Then King Solomon swore an oath by Jehovah, saying: 'May God curse me and add to it if AdoniJah hasn't spoken these words against his own life. 24 And now, as Jehovah lives (He who established me, set me on the throne of my father David, and made me a house, just as the Lord said); today, AdoniJah will be put to death!'
25 So King Solomon sent out BenaiJah (the son of JehoiAda) to kill him, and AdoniJah died that day.

These are my thoughts, please share yours.
23 Solomon was willing to have Adonijah killed because of the request he made. Adonijah may have been trying to capture the throne by other means.
24 Solomon was going to no longer allow Adonijah be a problem, some times we have to remove our problems, this does not mean will kill them but sometimes we have to hand them over to the proper authorities to deal with which Solomon was king so he had to make the decision himself. Sometimes we have been trying to keep us from being where the Lord wants us.
25 Solomon no longer would be stopped from being king as the Lord had wanted.