2 Chronicles 35:14-15

14And afterward they made ready for themselves, and for the priests: because the priests the sons of Aaron were busied in offering of 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 porters waited at every gate; they might not depart from their service; for their brethren the Levites prepared for them.1