Numbers 4:18-20

18“Do not allow the Kohathite tribal clans to be wiped out from the Levites.

19Do this for them so that they may live and not die when they come near the most holy objects: Aaron and his sons are to go in and assign each man his task and transportation duty.

20The Kohathites are not to go in and look at the holy objects as they are covered or they will die.”