Of God and His Creatures

But what was the use of this promise to men who were never to live to see the salvation of Christ? Were they to die in their sins? It is commonly replied that circumcision, the chief of the Sacraments of the Old Law, took away original sin, not of itself, but by virtue of the faith of them that performed it; whereas baptism is effectual of itself, even when conferred by a minister who does not believe in it, providing he confers it seriously and without maiming the rite.

Of God and His Creatures: 4.57