Dei Filius, On Faith, Canon 3

3. If any one shall say that divine revelation can not be made credible by outward signs, and therefore that men ought to be moved to faith solely by the internal experience of each, or by private inspiration: let him be anathema.

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