Exodus 24:15-18

Then Moses went up on the mountain, and the cloud covered the mountain. The glory of the LORD dwelt 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. 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. Moses entered the cloud and went up on the mountain. And Moses was on the mountain forty days and forty nights.