Exodus 24:15-18

Moses went up Mount Sinai, and a cloud covered it. The dazzling light of the LORD's presence came down on the mountain. To the Israelites the light looked like a fire burning on top of the mountain. The cloud covered the mountain for six days, and on the seventh day the LORD called to Moses from the cloud. Moses went on up the mountain into the cloud. There he stayed for forty days and nights.