1 Esdras 1:15

15 The holy singers also, the sons of Asaph, were in their order, according to the appointment of David, to wit, Asaph, Zacharias, and Jeduthun, who was of the king's retinue.

1 Esdras 1:15 In-Context

13 And set them before all the people: and afterward they prepared for themselves, and for the priests their brethren, the sons of Aaron.
14 For the priests offered the fat until night: and the Levites prepared for themselves, and the priests their brethren, the sons of Aaron.
15 The holy singers also, the sons of Asaph, were in their order, according to the appointment of David, to wit, Asaph, Zacharias, and Jeduthun, who was of the king's retinue.
16 Moreover the porters were at every gate; it was not lawful for any to go from his ordinary service: for their brethren the Levites prepared for them.
17 Thus were the things that belonged to the sacrifices of the Lord accomplished in that day, that they might hold the passover,
The King James Version is in the public domain.