Numbers 3:10, 38

You are to appoint Aaron and his sons to carry out their priestly responsibilities, but any unauthorized person who comes near the sanctuary is to be put to death.”

Moses, Aaron, and his sons, who performed the duties of  the sanctuary as a service on behalf of the Israelites, camped in front of the tabernacle on the east,  in front of the tent of meeting toward the sunrise. Any unauthorized person who came near it was to be put to death.