Numbers 4:16-20

16And to the office of Eleazar the son of Aaron the priest pertaineth the oil for the light, and the sweet incense, and the daily meat offering, and the anointing oil, and the oversight of all the tabernacle, and of all that is in it, in the sanctuary, and in its vessels. 17And the LORD spoke to Moses and to Aaron, saying, 18Cut ye not off the tribe of the families of the Kohathites from among the Levites: 19But 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 every one to his service and to his burden: 20But they shall not go in to see when the holy things are covered, lest they die.