2 Chronicles 35:14-15

14And afterwards they made ready for themselves and for the priests; because the priests, the sons of Aaron, [were engaged] in offering up the burnt-offerings and the fat until night; therefore the Levites prepared for themselves, and for the priests, the sons of Aaron.

15And the singers, the sons of Asaph, were in their place, according to the commandment of David, and Asaph, and Heman, and Jeduthun the king's seer; and the doorkeepers were at every gate; they had not to depart from their service, for their brethren the Levites prepared for them.