Numbers 8:22-24

New Revised Standard Version Catholic Edition

²² Thereafter the Levites went in to do their service in the tent of meeting in attendance on Aaron and his sons. As the Lord had commanded Moses concerning the Levites, so they did with them.

²³ The Lord spoke to Moses, saying: ²⁴ This applies to the Levites: from twenty-five years old and upward they shall begin to do duty in the service of the tent of meeting;