Exodus 19:20-22

The LORD came down on Mount Sinai, to the top of the mountain; and the LORD called Moses to the top of the mountain, and Moses went up. Then the LORD spoke to Moses, “Go down, warn the people, so that they do not break through to the LORD to gaze, and many of them perish. Also let the priests who come near to the LORD consecrate themselves, or else the LORD will break out against them.”