Exodus 19:13

10 And the LORD said unto Moses, Go unto the people, and sanctify them to day and to morrow, and let them wash their clothes,

11 And be ready against the third day: for the third day the LORD will come down in the sight of all the people upon mount Sinai.

12 And thou shalt set bounds unto the people round about, saying, Take heed to yourselves, that ye go not up into the mount, or touch the border of it: whosoever toucheth the mount shall be surely put to death:

13 There shall not an hand touch it, but he shall surely be stoned, or shot through; whether it be beast or man, it shall not live: when the trumpet soundeth long, they shall come up to the mount.

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

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

16 And 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.