Exodus 24:15-18

Then Moses went up to the mountain, and the cloud covered the mountain. The glory of the LORD rested on Mount Sinai, and the cloud covered it for six days; and on the seventh day He called to Moses from the midst of the cloud. And to the eyes of the sons of Israel the appearance of the glory of the LORD was like a consuming fire on the mountain top. Moses entered the midst of the cloud as he went up to the mountain; and Moses was on the mountain forty days and forty nights.