On the third new moon after the people of Israel had gone forth out of the land of Egypt, on that day they came into the wilderness of Sinai. And when they set out from Rephidim and came into the wilderness of Sinai, they encamped in the wilderness; and there Israel encamped before the mountain. And Moses went up to God, and the Lord called to him out of the mountain, saying, “Thus you shall say to the house of Jacob, and tell the people of Israel: You have seen what I did to the Egyptians, and how I bore you on eagles’ wings and brought you to myself. Now therefore, if you will obey my voice and keep my covenant, you shall be my own possession among all peoples; for all the earth is mine, and you shall be to me a kingdom of priests and a holy nation. These are the words which you shall speak to the children of Israel.” So Moses came and called the elders of the people, and set before them all these words which the Lord had commanded him. And all the people answered together and said, “All that the Lord has spoken we will do.” And Moses reported the words of the people to the Lord. And the Lord said to Moses, “Lo, I am coming to you in a thick cloud, that the people may hear when I speak with you, and may also believe you for ever.”
Then Moses told the words of the people to the Lord. And the Lord said to Moses, “Go to the people and consecrate them today and tomorrow, and let them wash their garments, and be ready by the third day; for on the third day the Lord will come down upon Mount Sinai in the sight of all the people. And you shall set bounds for the people round about, saying, ”Take heed that you do not go up into the mountain or touch the border of it; whoever touches the mountain shall be put to death; no hand shall touch him, but he shall be stoned or shot; whether beast or man, he shall not live.’ When the trumpet 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. And he said to the people, “Be ready by the third day; do not go near a woman.”
On the morning of the third day there were thunders and lightnings, and a thick cloud upon the mountain, and a very loud trumpet blast, so that all the people who were in the camp trembled.
–Exodus 19:1-16