We, with the authority of our Lord Jesus Christ, the blessed Apostles Peter and Paul, and with our own, do declare, pronounce and define that the doctrine which holds that the Virgin Mary was, in the first instant of her conception, preserved untouched by any taint of original guilt [sin], by a singular grace and privilege of Almighty God, in consideration of the merits of Christ Jesus the Savior of mankind — that this doctrine was revealed by God and therefore is to be firmly and steadfastly believed by all the faithful. Wherefore if any shall presume (which God forbid) to think in their hearts anything contrary to this definition of ours, let them realize and know well that they are condemned by their own judgment …
Ineffabilis Deus, December 8, 1854, from Documents of the Christian Church, p. 286 – Mary’s Immaculate Conception
– Mary’s Immaculate Conception