Dei Filius, On Faith and Reason, Canon 1

IV.

On Faith and Reason.

1. If any one shall say that in divine revelation there are no mysteries, truly and properly so called, but that all the doctrines of faith can be understood and demonstrated from natural principles, by properly cultivated reason: let him be anathema.

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