Numbers 18:3-5

New Revised Standard Version, Anglicised

³ They shall perform duties for you and for the whole tent. But they must not approach either the utensils of the sanctuary or the altar, otherwise both they and you will die. ⁴ They are attached to you in order to perform the duties of the tent of meeting, for all the service of the tent; no outsider shall approach you. ⁵ You yourselves shall perform the duties of the sanctuary and the duties of the altar, so that wrath may never again come upon the Israelites.