Augustine
Augustine is often misrepresented as having believed in the sinlessness of Mary. The Anglican scholar J.N.D. Kelly explains:
“he [Augustine] did not hold (as has sometimes been alleged) that she [Mary] was born exempt from all taint of original sin (the later doctrine of the immaculate conception). Julian of Eclanum maintained this as a clinching argument in his onslaught on the whole idea of original sin, but Augustine’s rejoinder was that Mary had indeed been born subject to original sin like all other human beings, but had been delivered from its effects ‘by the grace of rebirth’.” (Early Christian Doctrines [San Francisco, California: HarperCollins Publishers, 1978], p. 497)
Augustine wrote the following about Christ being the only post-Adamic human conceived without original sin. He approvingly quotes another church father, Ambrose. Notice that one of his quotes of Ambrose specifically mentions Mary, so it can’t be argued that they didn’t have Mary in mind at the time that they wrote. After quoting Ambrose, Augustine comments that Ambrose’s view is the view held by the universal church of his day, a view supported by “the catholic faith”:
“And now that we are about to bring this book to a conclusion, we think it proper to do on this subject of Original Sin what we did before in our treatise On Grace, --adduce in evidence against the injurious talk of these persons that servant of God, the Archbishop Ambrose, whose faith is proclaimed by Pelagius to be the most perfect among the writers of the Latin Church; for grace is more especially honoured in doing away with original sin. In the work which the saintly Ambrose wrote, Concerning the Resurrection, he says: ‘I fell in Adam, in Adam was I expelled from Paradise, in Adam I died; and He does not recall me unless He has found me in Adam,–so as that, as I am obnoxious to the guilt of sin in him, and subject to death, I may be also justified in Christ.’ Then, again, writing against the Novatians, he says: ‘We men are all of us born in sin; our very origin is in sin; as you may read when David says, ‘Behold, I was shapen in iniquity, and in sin did my mother conceive me.’ Hence it is that Paul’s flesh is ‘a body of death;’ even as he says himself, ‘Who shall deliver me from the body of this death?’ Christ’s flesh, however, has condemned sin, which He experienced not by being born, and which byy dying He crucified, that in our flesh there might be justification through grace, where previously there was impurity through sin.’ The same holy man also, in his Exposition Isaiah, speaking of Christ, says: ‘Therefore as man He was tried in all things, and in the likeness of men He endured all things; but as born of the Spirit, He was free from sin. For every man is a liar, and no one but God alone is without sin. It is therefore an observed and settled fact, that no man born of a man and a woman, that is, by means of their bodily union, is seen to be free from sin. Whosoever, indeed, is free from sin, is free also from a conception and birth of this kind.’ Moreover, when expounding the Gospel according to Luke, he says: ‘It was no cohabitation with a husband which opened the secrets of the Virgin’s womb; rather was it the Holy Ghost which infused immaculate seed into her unviolated womb. For the Lord Jesus alone of those who are born of woman is holy, inasmuch as He experienced not the contact of earthly corruption, by reason of the novelty of His immaculate birth; nay, He repelled it by His heavenly majesty.’ These words, however, of the man of God are contradicted by Pelagius, notwithstanding all his commendation of his author, when he himself declares that ‘we are procreated, as without virtue, so without vice.’ What remains, then, but that Pelagius should condemn and renounce this error of his; or else be sorry that he has quoted Ambrose in the way he has? Inasmuch, however, as the blessed Ambrose, catholic bishop as he is, has expressed himself in the above-quoted passages in accordance with the catholic faith, it follows that Pelagius, along with his disciple Coelestius, was justly condemned by the authority of the catholic Church for having turned aside from the true way of faith, since he repented not for having bestowed commendation on Ambrose, and for having at the same time entertained opinions in opposition to him.” (On the Grace of Christ, and on Original Sin, 2:47-48)