Exodus 19:10-12

10And the LORD said to Moses, “Go to the people and consecrate them today and tomorrow. Have them wash their clothes 11and 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. 12Put 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.