Exodus 19:12-13

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.”