Numbers 4:18-20

18“Don’t let the Kohathite families from Levi’s tribe be destroyed.

19This is what you must do so that they won’t die when they come near the most holy things: Aaron and his sons will go into the holy place and tell each man what he will do and what he will carry.

20But the Kohathites must not go in to look at the holy things, even for a moment, or they will die.”