Dei Filius, On Faith, Canon 6

6. If any one shall say that the condition of the faithful, and of those who have not yet attained to the only true faith, is on a par, so that Catholics may have just cause for doubting, with suspended assent, the faith which they have already received under the magisterium of the Church, until they shall have obtained a scientific demonstration of the credibility and truth of their faith: let him be anathema.

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