2 Chronicles 35:14-15

14Afterward they prepared for themselves and for the priests, because the priests, the sons of Aaron, were 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 at their positions 1according to the command of David, Asaph, Heman, and Jeduthun the king’s seer; and 2the gatekeepers at each gate did not have to leave their service, because their kinsmen the Levites prepared for them.