Numbers 4:28-30

American Standard Version

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; ³⁰ from thirty years old and upward even unto fifty years old shalt thou number them, every one that entereth upon the service, to do the work of the tent of meeting.