Exodus 19:12-16

You shall set bounds 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 surely be put to death. No hand shall touch him, but he shall surely be stoned or shot through; whether beast or man, he shall not live.’ When the ram’s horn sounds a long blast, they shall come up to the mountain.” So Moses went down from the mountain to the people and consecrated the people, and they washed their garments. He said to the people, “Be ready for the third day; do not go near a woman.” So it came about on the third day, when it was morning, that there were thunder and lightning flashes and a thick cloud upon the mountain and a very loud trumpet sound, so that all the people who were in the camp trembled.