Fasting: Prolonged for Forty Days, by Moses
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Exodus 24:18
Moses entered the cloud as he went up on the mountain, and he remained on the mountain forty days and forty nights.
Exodus 34:28
So Moses was there with the LORD forty days and forty nights without eating bread or drinking water. He wrote on the tablets the words of the covenant—the Ten Commandments.
Deuteronomy 9:9, 18
When I went up on the mountain to receive the tablets of stone, the tablets of the covenant that the LORD made with you, I stayed on the mountain forty days and forty nights. I ate no bread and drank no water. / Then I fell down before the LORD for forty days and forty nights, as I had done the first time. I did not eat bread or drink water because of all the sin you had committed in doing what was evil in the sight of the LORD and provoking Him to anger.