Exodus 24:16-18 Amplified Bible, Classic Edition (AMPC)
16 The glory of the Lord rested on Mount Sinai, and the cloud covered it for six days. On the seventh day [God] called to Moses out of the midst of the cloud.
17 And the glory of the Lord appeared to the Israelites like devouring fire on the top of the mountain.
18 Moses entered into the midst of the cloud and went up the mountain, and Moses was on the mountain forty days and nights.