Exodus 24:15-18

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. Now the appearance of the glory of the LORD was like a consuming fire on the top of the mountain to the eyes of the children of Israel. Moses went into the midst of the cloud and went up to the mountain. And Moses was on the mountain for forty days and forty nights.