Numbers 4:19-21 New American Standard Bible (NASB)

19. But do this to them that they may 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;

20. but they shall not go in to see the holy objects even for a moment, or they will die."

21. Then the Lord spoke to Moses, saying,

Numbers 4