Augustine of Hippo — as excerpted in the Catena Aurea on Matthew 12:38-40

“(De Cons. Ev. iii. 24.) Some, not knowing the Scripture manner of speaking, would interpret as one night those three hours of darkness when the sun was darkened from the sixth to the ninth hour; and as a day in like manner those other three hours in which it was again restored to the world, from the ninth hour till sunset. Then follows the night preceding the sabbath, which if we reckon with its own day we shall have thus two days and two nights. Then after the sabbath follows the night of the sabbath prime, that is of the dawning of the Lord’s day on which the Lord arose. Thus we shall only get two nights and two days, with this one night to be added if we might understand the whole of it, and it could not be shewn that that dawn was indeed the latter part of the night. So that not even by taking in those six hours, three of darkness, and three of restored light, can we establish the computation of three days and three nights. It remains therefore that we find the explanation in that usual manner of Scripture of putting a part for the whole.”