Exodus 24:12-18 New Revised Standard Version (NRSV)
12 The Lord said to Moses, “Come up to me on the mountain, and wait there; and I will give you the tablets of stone, with the law and the commandment, which I have written for their instruction.” 13 So Moses set out with his assistant Joshua, and Moses went up into the mountain of God. 14 To the elders he had said, “Wait here for us, until we come to you again; for Aaron and Hur are with you; whoever has a dispute may go to them.”
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 for six days; on the seventh day he called to Moses out 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 Moses entered the cloud, and went up on the mountain. Moses was on the mountain for forty days and forty nights.