Exodus 24:15-18

Then Moses went up to the mountain, and the cloud covered the mountain. The glory and brilliance of the LORD rested on Mount Sinai, and the cloud covered it for six days. On the seventh day God called to Moses from the midst of the cloud. In the sight of the Israelites the appearance of the glory and brilliance of the LORD was like consuming fire on the top of the mountain. Moses entered the midst of the cloud and went up the mountain; and he was on the mountain forty days and forty nights.