Exodus 24:15-18

Then Moses climbed up the mountain, and the cloud covered it. And the glory of the LORD settled down on Mount Sinai, and the cloud covered it for six days. On the seventh day the LORD called to Moses from inside the cloud. To the Israelites at the foot of the mountain, the glory of the LORD appeared at the summit like a consuming fire. Then Moses disappeared into the cloud as he climbed higher up the mountain. He remained on the mountain forty days and forty nights.