Nehemiah 12:45
that they stood and waited upon the office of their God, and the office of the purification. And the singers and porters stood after the commandment of David and of Solomon his son:
1 Chronicles 25:1-26
And David and the captains of the host appointed out to do service, the sons of Asaph of Heman and Jeduthun, which did prophesy with harps, psalteries and cymbals. And they were numbered unto the work according to their office.
1 Chronicles 23:28
"To wait at the hands of the sons of Aaron in the service of the house of the LORD, and to have the oversight of the courts and of the store houses, and of the purifying of all holy things, and of the work of the things that served for the house of God,
2 Chronicles 23:6
And there shall none come into the house of the LORD, save the priests and the Levites that minister. They shall go in, for they are holy: and all the people shall keep the watch of the LORD.