Augustine of Hippo, On the Holy Trinity III.6: Diversity Alone Makes a Miracle

And who is it that restored to the corpses their proper souls when the dead rose again, unless He who gives life to the flesh in the mother’s womb, in order that they may come into being who yet are to die? But when such things happen in a continuous kind of river of ever-flowing succession, passing from the hidden to the visible, and from the visible to the hidden, by a regular and beaten track, then they are called natural; when, for the admonition of men, they are thrust in by an unusual changeableness, then they are called miracles.