Numbers 8:24-26

International Standard Version

²⁴ “Now regarding a descendant of Levi who is 25 years and above, he is to enter work in the service at the appointed place of meeting, ²⁵ but starting at 50 years of age, he is to retire from service and is no longer to work. ²⁶ He may minister to his brothers at the Tent of Meeting by keeping watch, but he is not to engage in service. This is how you are to act with respect to the obligations of the descendants of Levi.”