Exodus 24:12; Exodus 24:15-18

12 The LORD said to Moses, "Come up to me on the mountain, and wait there; and I will give you the tables of stone, with the law and the commandment, which I have written for their instruction."
15 Then Moses went up on the mountain, and the cloud covered the mountain. 16 The glory of the LORD settled on Mount Sinai, and the cloud covered it six days; and on the seventh day he called to Moses out of the midst of the cloud. 17 Now the appearance of the glory of the LORD was like a devouring fire on the top of the mountain in the sight of the people of Israel. 18 And Moses entered the cloud, and went up on the mountain. And Moses was on the mountain forty days and forty nights.