And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
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Hippolytus of Rome
He did not say night and day, but one day, with reference to the name of the light. He did not say the first day; for if he had said the first day, he would also have had to say that the second day was made. But it was right to speak not of the first day, but of one day, in order that by saying one, he might show that it returns on its orbit and, while it remains one, makes up the week.