Nehemiah

Moreover David and the captains of the host separated to the service of the sons of Asaph, and of Heman, and of Jeduthun, who should prophesy with harps, with psalteries, and with cymbals: and the number of the workmen according to their service was:

The nineteenth to Mallothi, he, his sons, and his brethren, were twelve:

But let none come into the house of the Lord, save the priests, and they that minister of the Levites; they shall go in, for they are holy: but all the people shall keep the watch of the Lord.

Because their office was to wait on the sons of Aaron for the service of the house of the Lord, in the courts, and in the chambers, and in the purifying of all holy things, and the work of the service of the house of God;

And they ministered before the dwelling place of the tabernacle of the congregation with singing, until Solomon had built the house of the Lord in Jerusalem: and then they waited on their office according to their order.