Exodus 19:9, 20, 24

The LORD said to Moses, “Behold, I will come to you in a thick cloud, so that the people may hear when I speak with you and may believe and trust in you forever.” Then Moses repeated the words of the people to the LORD.

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 he went up.

Then the LORD said to him, “Go down and come up again, you and Aaron with you; but do not let the priests and the people break through [the barriers] to come up to the LORD, or He will break forth [in judgment] against them [and destroy them].”