Dei Filius, On Faith, Canon 4

4. If any one shall say that miracles are impossible, and therefore that all the accounts regarding them, even those contained in Holy Scripture, are to be dismissed as fabulous or mythical; or that miracles can never be known with certainty, and that the divine origin of Christianity can not be proved by them: let him be anathema.

Translation: Henry Edward Manning, Petri Privilegium (1871), reproduced in Philip Schaff, Creeds of Christendom II, via CCEL.