Exodus 19:10-13

10 the Lord said to Moses: "Go to the people and consecrate them today and tomorrow. Have them wash their clothes
11 and prepare for the third day, because on the third day the Lord will come down upon Mount Sinai in the sight of all the people.
12 You shall set limits for the people all around, saying, "Be careful not to go up the mountain or to touch the edge of it. Any who touch the mountain shall be put to death.
13 No hand shall touch them, but they shall be stoned or shot with arrows; whether animal or human being, they shall not live.' When the trumpet sounds a long blast, they may go up on the mountain."