Numbers 4:33-35

American Standard Version

³³ This is the service of the families of the sons of Merari, according to all their service, in the tent of meeting, under the hand of Ithamar the son of Aaron the priest.

³⁴ And Moses and Aaron and the princes of the congregation numbered the sons of the Kohathites by their families, and by their fathers’ houses, ³⁵ from thirty years old and upward even unto fifty years old, every one that entered upon the service, for work in the tent of meeting: