Numbers 3:10; Numbers 3:38

10 "So you shall appoint Aaron and his sons that they may keep their priesthood, but the layman who comes near shall be put to death."

38 Now those who were to camp before the tabernacle eastward, before the tent of meeting toward the sunrise, are Moses and Aaron and his sons, performing the duties of the sanctuary for the obligation of the sons of Israel; but the layman coming near was to be put to death.