2 Chronicles 35:15

The singers, the descendants of Asaph, were at their stations according to the command of David, Asaph, Heman, and Jeduthun the king’s seer. And the gatekeepers at each gate did not need to leave their posts, because their fellow Levites made preparations for them.

And 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.