2 Chronicles 35:15 ESV

15 The singers, the sons of Asaph, were in their place 1according to the command of David, and Asaph, and Heman, and Jeduthun the king's 2seer; 3and the gatekeepers were at each gate. They did not need to depart from their service, for their brothers the Levites prepared for them.

References for 2 Chronicles 35:15