Exodus 19:14

10 Then the LORD said to Moses, “Go to the people and consecrate them today and tomorrow. They must wash their clothes

11 and be prepared by the third day, for on the third day the LORD will come down on Mount Sinai in the sight of all the people.

12 And you are to set up a boundary for the people around the mountain and tell them, ‘Be careful not to go up on the mountain or touch its base. Whoever touches the mountain shall surely be put to death.

13 No hand shall touch him, but he shall surely be stoned or shot with arrows—whether man or beast, he must not live.’ Only when the ram’s horn sounds a long blast may they approach the mountain.”

14 When Moses came down from the mountain to the people, he consecrated them, and they washed their clothes.

15 “Be prepared for the third day,” he said to the people. “Do not draw near to a woman.”

16 On the third day, when morning came, there was thunder and lightning. A thick cloud was upon the mountain, and a very loud blast of the ram’s horn went out, so that all the people in the camp trembled.

17 Then Moses brought the people out of the camp to meet with God, and they stood at the foot of the mountain.

18 Mount Sinai was completely enveloped in smoke, because the LORD had descended on it in fire. And the smoke rose like the smoke of a furnace, and the whole mountain quaked violently.

Read all of Exodus 19