Numbers 4:28-30

New Revised Standard Version, Anglicised

²⁸ This is the service of the clans of the Gershonites relating to the tent of meeting, and their responsibilities are to be under the oversight of Ithamar son of Aaron the priest.

²⁹ As for the Merarites, you shall enrol them by their clans and their ancestral houses; ³⁰ from thirty years old up to fifty years old you shall enrol them, everyone who qualifies to do the work of the tent of meeting.