Exodus 19:9, 20, 24

Then the LORD said to Moses, “I will come to you in a thick cloud, Moses, so the people themselves can hear me when I speak with you. Then they will always trust you.” Moses told the LORD what the people had said.

The LORD came down on the top of Mount Sinai and called Moses to the top of the mountain. So Moses climbed the mountain.

But the LORD said, “Go down and bring Aaron back up with you. In the meantime, do not let the priests or the people break through to approach the LORD, or he will break out and destroy them.”