Exodus 24:15-18

And when Moses was gone up, a cloud covered the mount. And the glory of the Lord dwelt upon Sinai, covering it with a cloud six days: and the seventh day he called him out of the midst of the cloud. And the sight of the glory of the Lord was like a burning fire upon the top of the mount, in the eyes of the children of Israel. And Moses, entering into the midst of the cloud, went up into the mountain: and he was there forty days, and forty nights.