For how can anything done by the will of God be contrary to nature, when the will of so great a creator constitutes the nature of each created thing? A portent therefore happens not contrary to nature, but contrary to what is known of nature.

[Quo modo est enim contra naturam, quod Dei fit uoluntate, cum uoluntas tanti utique conditoris conditae rei cuiusque natura sit? Portentum ergo fit non contra naturam, sed contra quam est nota natura.]

Augustine of Hippo (354-430) Christian church father, philosopher, saint [b. Aurelius Augustinus]

City of God [De Civitate Dei], Book 21, ch. 8 (21.8) (AD 412-416) [tr. Green (Loeb) (1972)]
    (Source)

Commonly: "Miracles are not contrary to nature, but only contrary to what we know about nature."

(Source (Latin)). Alternate translations:

For how is that contrary to nature which happens by the will of God, since the will of so mighty a Creator is certainly the nature of each created thing? A portent, therefore, happens not contrary to nature, but contrary to what we know as nature.
[tr. Dods (1871)]

Nothing that happens by the will of God can be ‘contrary to nature.’ The ‘nature’ of any particular created thing is precisely what the supreme Creator of the thing willed it to be. Hence, a portent is merely contrary to nature as known, not to nature as it is.
[tr. Walsh/Honan (1954)]

For how can an event be contrary to nature when it happens by the will of God, since the will of the great Creator assuredly is the nature of every created thing? A portent, therefore, does not occur contrary to nature, but contrary to what is known of nature.
[tr. Bettenson (1972)]