Numbers 4:17-21

Then the Lord spoke to Moses and to Aaron, saying,

“Do not let the tribe of the families of the Kohathites be eliminated from among the Levites.

Rather, do this for them so that they will live and not die when they approach the most holy objects: Aaron and his sons shall go in and assign each of them to his work and to his load;

but they shall not come in to see the holy objects even for a moment, or they will die.” Duties of the Gershonites

Then the Lord spoke to Moses, saying,