Proclamation of the Dogma of the Immaculate Conception

Source: fides.org

Pope Pius IX, December 8, 1854:

We declare, pronounce, and define that the doctrine which holds that the Blessed Virgin Mary, from the first instant of her Conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Savior of the human race, was preserved free and exempt from all stain of original sin, is revealed by God, and therefore must be firmly and constantly believed by all the faithful.

Therefore, if any should presume, God forbid, to think in their hearts otherwise than what has been defined by Us, let them know and understand that, condemned by their own judgment, they have suffered shipwreck in the faith and have separated themselves from the unity of the Church; and furthermore, that if by word, by writing, or by any other external means they should dare to express these sentiments of their heart, they would thereby incur the penalties established by law.