Exodus 19:9-13

Then the Lord said to Moses, “Behold, I will come to you in a thick cloud, so that the people may hear when I speak with you and may also trust in you forever.” Then Moses told the words of the people to the Lord.

The Lord also said to Moses, “Go to the people and consecrate them today and tomorrow, and have them wash their garments;

and have them ready for the third day, for on the third day the Lord will come down on Mount Sinai in the sight of all the people.

But you shall set boundaries for the people all around, saying, ‘Beware that you do not go up on the mountain or touch the border of it; whoever touches the mountain shall certainly be put to death.

No hand shall touch him, but he shall certainly be stoned or shot through; whether animal or person, the violator shall not live.’ When the ram’s horn sounds a long blast, they shall come up to the mountain.”