Augustine on original sin and the Blessed Mother:
We must except the Holy Virgin Mary, concerning whom I wish to raise no question when it touches the subject of sins, out of honor to the Lord; for from Him we know what abundance of grace for overcoming sin in every particular was conferred upon her who had the merit to conceive and bear Him who undoubtedly had no sin (Nature and Grace 36:42).
Like Augustine, Martin Luther also affirmed that the Blessed Virgin Mary was preserved from original sin “from the very moment she began to live”:
“But the other conception, namely the infusion of the soul, it is piously and suitably believed, was without any sin, so that while the soul was being infused, she would at the same time be cleansed from original sin and adorned with the gifts of God to receive the holy soul thus infused. And thus, in the very moment in which she began to live, she was without all sin.” (Martin Luther, Weimar edition of Martin Luther’s Works, trans. and ed. J. Pelikan. Concordia: St. Louis, Volume 4, 694)
It is quite remarkable that Luther got the immaculate conception correct. This is likely because Luther drank deeply of the nominalists who were Franciscans. The Franciscans at that time were generally proponents of the doctrine of the Immaculate Conception.