Numbers 3:38

3:38 But those who were to camp in front of the tabernacle on the east, in front of the tent of meeting, were Moses, Aaron, and his sons. They were responsible for the needs of the sanctuary and for the needs of the Israelites, but the unauthorized person who approached was to be put to death.

Numbers 8:26

8:26 They may assist their colleagues in the tent of meeting, to attend to needs, but they must do no work. This is the way you must establish the Levites regarding their duties.”