Numbers 4:18-21 American Standard Version (ASV)

18. Cut ye not off the tribe of the families of the Kohathites from among the Levites;

19. but 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;

20. but they shall not go in to see the sanctuary even for a moment, lest they die.

21. And Jehovah spake unto Moses, saying,

Numbers 4