Numbers 4:26

23 from thirty years old and upward until fifty years old shalt thou number them; all that enter in to wait upon the service, to do the work in the tent of meeting.

24 This is the service of the families of the Gershonites, in serving and in bearing burdens:

25 they shall bear the curtains of the tabernacle, and the tent of meeting, its covering, and the covering of sealskin that is above upon it, and the screen for the door of the tent of meeting,

26 and the hangings of the court, and the screen for the door of the gate of the court, which is by the tabernacle and by the altar round about, and their cords, and all the instruments of their service, and whatsoever shall be done with them: therein shall they serve.

27 At the commandment of Aaron and his sons shall be all the service of the sons of the Gershonites, in all their burden, and in all their service; and ye shall appoint unto them in charge all their burden.

28 This is the service of the families of the sons of the Gershonites in the tent of meeting: and their charge shall be under the hand of Ithamar the son of Aaron the priest.

29 As for the sons of Merari, thou shalt number them by their families, by their fathers` houses;