2 Samuel 5:3-5

When all the elders of Israel had come to King David at Hebron, the king made a covenant with them at Hebron before the LORD, and they anointed David king over Israel. David was thirty years old when he became king, and he reigned forty years. In Hebron he reigned over Judah seven years and six months, and in Jerusalem he reigned over all Israel and Judah thirty-three years.