Exodus 34:28

34:28 So he was there with the Lord forty days and forty nights; he did not eat bread, and he did not drink water. He wrote on the tablets the words of the covenant, the ten commandments.

Deuteronomy 9:18-19

9:18 Then I again fell down before the Lord for forty days and nights; I ate and drank nothing because of all the sin you had committed, doing such evil before the Lord as to enrage him. 9:19 For I was terrified at the Lord’s intense anger that threatened to destroy you. But he listened to me this time as well.