Numbers 3:10; Numbers 3:38

10 And you shall appoint Aaron and his sons, and they shall guard their priesthood. But if any outsider comes near, he shall be put to death."

38 Those who were to camp before the tabernacle on the east, before the tent of meeting toward the sunrise, were Moses and Aaron and his sons, guarding the sanctuary itself, to protect the people of Israel. And any outsider who came near was to be put to death.