Exodus 24:16-18

24:16 The glory of the Lord resided on Mount Sinai, and the cloud covered it for six days. On the seventh day he called to Moses from within the cloud. 24:17 Now the appearance of the glory of the Lord was like a devouring fire on the top of the mountain in plain view of the people. 24:18 Moses went into the cloud when he went up the mountain, and Moses was on the mountain forty days and forty nights.