Exodus 19:10-13

10The Lord also said to Moses, “Go to the people and consecrate them today and tomorrow [that is, prepare them for My sacred purpose], and have them wash their clothes

11and be ready by the third day, because on the third day the Lord will come down on Mount Sinai [in the cloud] in the sight of all the people.

12You 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.

13No 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.”