Exodus 19:18

14And Moses went down from the mount unto the people, and sanctified the people; and they washed their clothes.

15And he said unto the people, Be ready against the third day: come not at your wives.

16And it came to pass on the third day in the morning, that there were thunders and lightnings, and a thick cloud upon the mount, and the voice of the trumpet exceeding loud; so that all the people that was in the camp trembled.

17And Moses brought forth the people out of the camp to meet with God; and they stood at the nether part of the mount.

18And mount Sinai was altogether on a smoke, because the Lord descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly.

19And when the voice of the trumpet sounded long, and waxed louder and louder, Moses spake, and God answered him by a voice.

20And the Lord came down upon mount Sinai, on the top of the mount: and the Lord called Moses up to the top of the mount; and Moses went up.

21And the Lord said unto Moses, Go down, charge the people, lest they break through unto the Lord to gaze, and many of them perish.

22And let the priests also, which come near to the Lord, sanctify themselves, lest the Lord break forth upon them.