1 Kings 11:35

But I will take the kingdom out of his son’s hand, and will give it unto thee, even ten tribes.

The promise was given to Jeroboam by Ahijah the Shilonite when the two were alone together in the field, after Ahijah took his new garment and tore it into twelve pieces and told Jeroboam to take ten pieces for himself. God would rend the kingdom from Solomon and take it out of his son's hand to give ten tribes to Jeroboam. The taking would not occur during Solomon's lifetime, for he would remain prince all the days of his life, and the kingdom would be taken from his son only after Solomon's death at the end of his reign.

Solomon was permitted to keep the kingdom in his lifetime for the sake of David, God's chosen servant, because David had kept God's commandments, statutes and judgments. The division was decreed because Israel had forsaken God and worshiped Ashtoreth the goddess of the Zidonians, Chemosh the god of the Moabites, and Milcom the god of the Ammonites, and had not walked in God's ways to do what is right in His eyes and to keep His statutes and judgments as David had done. Jeroboam's elevation over the ten tribes is bound to the kingdom's later ruin, for his apostasy led Israel into sin and brought the foretold judgment of uprooting and scattering.