Numbers 4:17

When Aaron and his sons have finished covering the sanctuary, and all the furniture of the sanctuary, as the camp moves forward; after that, the sons of Kohath shall come to carry it: but they shall not touch the sanctuary, lest they die. These things are the burden of the sons of Kohath in the Tent of Meeting.

The duty of Eleazar the son of Aaron the priest shall be the oil for the light, the sweet incense, the continual meal offering, and the anointing oil, the requirements of all the tabernacle, and of all that is in it, the sanctuary, and its furnishings.

Don't cut off the tribe of the families of the Kohathites from among the Levites;

but thus do to them, that they may live, and not die, when they approach to the most holy things: Aaron and his sons shall go in, and appoint them everyone to his service and to his burden;