Exodus 34:27-29

Then the LORD said to Moses, “Write these words, for in accordance with these words I have made a covenant with you and with Israel.” Moses was there with the LORD forty days and forty nights; he ate no bread and drank no water. And He wrote on the tablets the words of the covenant, the Ten Commandments. When Moses came down from Mount Sinai with the two tablets of the Testimony in his hand, he did not know that the skin of his face was shining [with a unique radiance] because he had been speaking with God.