Shemoth (Exodus) 24:15-18

And Mosheh went up into the mountain, and a cloud covered the mountain. And the esteem of יהוה dwelt on Mount Sinai, and the cloud covered it for six days. And on the seventh day He called to Mosheh out of the midst of the cloud. And the appearance of the esteem of יהוה was like a consuming fire on the top of the mountain, before the eyes of the children of Yisra’ĕl. And Mosheh went into the midst of the cloud and went up into the mountain. And it came to be that Mosheh was on the mountain forty days and forty nights.