Numbers 4:16-20

16And the charge of Eleazar the son of Aaron the priest shall be the oil for the light, and the sweet incense, and the continual meal-offering, and the anointing oil, the charge of all the tabernacle, and of all that therein is, the sanctuary, and the furniture thereof.

17And Jehovah spake unto Moses and unto Aaron, saying, 18Cut ye not off the tribe of the families of the Kohathites from among the Levites; 19but thus do unto them, that they may live, and not die, when they approach unto the most holy things: Aaron and his sons shall go in, and appoint them every one to his service and to his burden; 20but they shall not go in to see the sanctuary even for a moment, lest they die.