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 position, because their fellow Levites made preparations for them.

1 Chronicles 25:1
Additionally, David and the commanders of the army set apart some of the sons of Asaph, Heman, and Jeduthun to prophesy with the accompaniment of lyres, harps, and cymbals. The following is the list of the men who performed this service:

1 Chronicles 26:12
These divisions of the gatekeepers, through their chief men, had duties for ministering in the house of the LORD, just as their brothers did.

2 Chronicles 30:16
They stood at their prescribed posts, according to the Law of Moses the man of God. The priests sprinkled the blood, which they received from the hand of the Levites.

2 Chronicles 35:14
Afterward, they made preparations for themselves and for the priests, since the priests, the descendants of Aaron, were offering up burnt offerings and fat until nightfall. So the Levites made preparations for themselves and for the priests, the descendants of Aaron.

2 Chronicles 35:16
So on that day the entire service of the LORD was carried out for celebrating the Passover and offering burnt offerings on the altar of the LORD, according to the command of King Josiah.

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 brothers the Levites prepared for them.