Exodus 19:11, 18, 20

and be ready against the third day: for the third day the LORD will come down in the sight of all the people upon mount Sinai.

And mount Sinai was altogether on a smoke, because the LORD descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly.

And the LORD came down upon mount Sinai, on the top of the mount: and the LORD called Moses up to the top of the mount; and Moses went up.