Everything David did as king, from beginning to end, is recorded in the records of Samuel the seer, the records of Nathan the prophet, and the records of Gad the seer.
King Hezekiah put the Levites in the Temple of the Lord with cymbals, harps, and lyres, as David, Gad, and Nathan had commanded. (Gad was the king’s seer, and Nathan was a prophet.) This command came from the Lord through his prophets.
(In the past, if someone in Israel wanted to ask something from God, he would say, “Let’s go to the seer.” We call the person a prophet today, but in the past he was called a seer.)