Exodus 19:12-19

You shall set barriers for the people all around [the mountain], saying, ‘Beware that you do not go up on the mountain or touch its border; whoever touches the mountain must be put to death. No hand shall touch him [that is, no one shall try to save the guilty party], but the offender must be stoned or shot through [with arrows]; whether man or animal [that touches the mountain], he shall not live.’ When the ram’s horn sounds a long blast, they shall come up to the mountain.” [Num 24:8] So Moses went down from the mountain to the people and sanctified them [for God’s sacred purpose], and they washed their clothes. He said to the people, “Be prepared for the third day; do not be intimate with a woman.” So it happened on the third day, when it was morning, that there were thunder and flashes of lightning, and a thick cloud was on the mountain, and a very loud blast was sounded on a ram’s horn, so that all the people who were in the camp trembled. Then Moses brought the people out of the camp to meet God, and they stood and presented themselves at the foot of the mountain. ORD Mount Sinai was wrapped in smoke because the LORD descended upon it in fire; its smoke ascended like the smoke of a furnace, and the whole mountain quaked violently. And it happened, as the blast of the ram’s horn grew louder and louder, Moses spoke and God answered him with [a voice of] thunder. [Deut 4:12]