1 Kings 1:30
Even as I sware unto thee by the LORD God of Israel, saying, Assuredly Solomon thy son shall reign after me, and he shall sit upon my throne in my stead; even so will I certainly do this day. Even as I sware unto thee by the LORD God of Israel, saying, Assuredly Solomon thy son shall reign after me, and he shall sit upon my throne in my stead; even so will I certainly do this day.
David reaffirmed his sworn oath that Solomon his son would assuredly reign after him and sit upon his throne in his place. That successor was the one appointed and directed by God to sit on Israel's throne. He declared that he would certainly carry out that oath that very day. He acted on the sworn promise by abdicating in Solomon's favor. Solomon was then anointed and proclaimed king, fulfilling the promised succession and thwarting Adonijah's rebellion and attempt to take the throne.