Exodus 19:9-16

9And the LORD said to Moses, Lo, I come to thee in a thick cloud, that the people may hear when I speak with thee, and believe thee for ever. And Moses told the words of the people to the LORD. 10And the LORD said to Moses, Go to the people, and sanctify them to day and to morrow, and let them wash their clothes, 11And be ready for the third day: for on the third day the LORD will come down in the sight of all the people upon mount Sinai. 12And thou shalt set bounds to the people all around, saying, Take heed to yourselves, that ye go not up upon the mount, or touch the border of it: whoever toucheth the mount shall be surely put to death: 13There 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.1 14And Moses went down from the mount to the people, and sanctified the people; and they washed their clothes. 15And he said to the people, Be ready for 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 were in the camp trembled.