2 Chronicles 35:14-15

14Afterward the Levites prepared for themselves and for the priests, because the priests, the sons of Aaron, were busy offering the burnt offerings and the fat until night; so the Levites prepared for themselves and for the priests, the sons of Aaron.

15The singers, the sons of Asaph, were also in their places in accordance with the command of David, Asaph, Heman, and Jeduthun the king’s seer; and the gatekeepers at each gate did not need to leave their service, because their kinsmen the Levites prepared for them.