Numbers 8:22-24

New Living Translation

²² After that the Levites went into the Tabernacle to perform their duties, assisting Aaron and his sons. So they carried out all the commands that the Lord gave Moses concerning the Levites.

²³ The Lord also instructed Moses, ²⁴ “This is the rule the Levites must follow: They must begin serving in the Tabernacle at the age of twenty-five,