Exodus 19:16; Exodus 19:21-24

16 So it came about on the third day, when it was morning, that there were thunder and lightning flashes and a thick cloud upon the mountain and a very loud trumpet sound, so that all the people who were in the camp trembled.

21 Then the LORD spoke to Moses, "Go down, warn the people, so that they do not break through to the LORD to gaze, and many of them perish.

22 "Also let the priests who come near to the LORD consecrate themselves, or else the LORD will break out against them."

23 Moses said to the LORD , "The people cannot come up to Mount Sinai, for You warned us, saying, 'Set bounds about the mountain and consecrate it.' "

24 Then the LORD said to him, "Go down and come up again, you and Aaron with you; but do not let the priests and the people break through to come up to the LORD , or He will break forth upon them."