Numbers 18:3-5

And they shall keep thy charge, and the charge of all the Tent: only they shall not come nigh unto the vessels of the sanctuary and unto the altar, that they die not, neither they, nor ye. And they shall be joined unto thee, and keep the charge of the tent of meeting, for all the service of the Tent: and a stranger shall not come nigh unto you. And ye shall keep the charge of the sanctuary, and the charge of the altar; that there be wrath no more upon the children of Israel.