Exodus 19:10-16

And the LORD said to Moses, “Go to the people and consecrate them today and tomorrow. Have them wash their clothes and be ready by the third day, because on that day the LORD will come down on Mount Sinai in the sight of all the people. Put limits for the people around the mountain and tell them, ‘Be careful that you do not approach the mountain or touch the foot of it. Whoever touches the mountain is to be put to death. They are to be stoned or shot with arrows; not a hand is to be laid on them. No person or animal shall be permitted to live.’ Only when the ram’s horn sounds a long blast may they approach the mountain.” After Moses had gone down the mountain to the people, he consecrated them, and they washed their clothes. Then he said to the people, “Prepare yourselves for the third day. Abstain from sexual relations.” On the morning of the third day there was thunder and lightning, with a thick cloud over the mountain, and a very loud trumpet blast. Everyone in the camp trembled.