Numbers 18:7

But as for you and your sons: guard the priesthood. For all that pertains to the service of the altar and of what is beyond the veil shall be exercised by the priests. If any outsider will approach, he shall be killed.

Other versions

King James Version

Therefore thou and thy sons with thee shall keep your priest's office for every thing of the altar, and within the vail; and ye shall serve: I have given your priest's office unto you as a service of gift: and the stranger that cometh nigh shall be put to death.

English Standard Version

And you and your sons with you shall guard your priesthood for all that concerns the altar and that is within the veil; and you shall serve. I give your priesthood as a gift, and any outsider who comes near shall be put to death."

New International Version

But only you and your sons may serve as priests in connection with everything at the altar and inside the curtain. I am giving you the service of the priesthood as a gift. Anyone else who comes near the sanctuary must be put to death."