Here we go:
**St. Athanasius **
. . . pure and unstained Virgin . . . (On the Incarnation of the Word, 8; Gambero, 102)
O noble Virgin, truly you are greater than any other greatness. For who is your equal in greatness, O dwelling place of God the Word? To whom among all creatures shall I compare you, O Virgin? You are greater than them all O Covenant, clothed with purity instead of gold! You are the Ark in which is found the golden vessel containing the true manna, that is, the flesh in which divinity resides. (Homily of the Papyrus of Turin, 71, 216; Gambero, 106)
St. Ephraem
Mary and Eve, two people without guilt, two simple people, were identical. Later, however, one became the cause of our death, the other the cause of our life (Op. syr. II, 327; Ott, 201)
The Virgin Mary is a symbol of the Church, when she receives the first announcement of the gospel . . . We call the Church by the name of Mary, for she deserves a double name. (Sermo ad noct. Resurr.; Gambero, 115)
Thou and thy mother are the only ones who are totally beautiful in every respect; for in thee, O Lord, there is no spot, and in thy Mother no stain. (Nisibene Hymns, 27, v. 8; Ott, 201)
Citing this source, J.N.D. Kelly asserts:
[W]e find Ephraem delineating her as free from every stain, like her son.
(Kelly, 495)
St. Cyril of Jerusalem
Pure and spotless is this birth. For where the Holy Spirit breathes, all pollution is taken away, so that the human birth of the Only-begotten from the Virgin is undefiled. (Catechetical Lectures, XII, 31-32; Gambero, 140)
St. Gregory Nazianzen
He was conceived by the Virgin, who had first been purified by the Spirit in soul and body; for, as it was fitting that childbearing should receive its share of honor, so it was necessary that virginity should receive even greater honor. (Sermon 38, 13; Gambero, 162-163)
St. Gregory of Nyssa
It was, to divulge by the manner of His Incarnation this great secret; that purity is the only complete indication of the presence of God and of His coming, and that no one can in reality secure this for himself, unless he has altogether estranged himself from the passions of the flesh. What happened in the stainless Mary when the fulness of the Godhead which was in Christ shone out through her, that happens in every soul that leads by rule the virgin life. (On Virginity, 2; NPNF 2, Vol. V, 344)
[T]he power of the Most High, through the Holy Spirit, overshadowed the human nature and was formed therein; that is to say, the portion of flesh was formed in the immaculate Virgin. (Against Apollinaris, 6; Gambero, 153)
St. Ambrose
. . . Mary, a Virgin not only undefiled but a Virgin whom grace has made inviolate, free of every stain of sin. (Commentary on Psalm 118, 22, 30; Jurgens, II, 166)
What is greater than the Mother of God? What more glorious than she whom Glory Itself chose? What more chaste than she who bore a body without contact with another body? (Virginity, II, 6; NPNF 2, Vol. X, 374)
St. Epiphanius
Mary, the holy Virgin, is truly great before God and men. For how shall we not proclaim her great, who held within her the uncontainable One, whom neither heaven nor earth can contain? (Panarion, 30, 31; Gambero, 127)
St. Jerome
‘There shall come forth a rod out of the stem of Jesse, and a flower shall grow out of his roots.’ The rod is the mother of the Lord–simple, pure, unsullied; drawing no germ of life from without but fruitful in singleness like God Himself… Set before you the blessed Mary, whose surpassing purity made her meet to be the mother of the Lord. (Letter XXII. To Eustochium, 19, 38; NPNF 2, Vol. VI, 29, 39; cf. Gambero, p. 213: “whose purity was so great that she merited to be the Mother of the Lord”)
Indeed how inferior they are, in terms of holiness, to blessed Mary, Mother of the Lord! (Contra Pelagianos, 1, 16; Gambero, 212)
St. Augustine
We must except the holy Virgin Mary, concerning whom I wish to raise no question when it touches the subject of sins, out of honour 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. Well, then, if, with this exception of the Virgin, we could only assemble together all the forementioned holy men and women, and ask them whether they lived without sin whilst they were in this life, what can we suppose would be their answer? (A Treatise on Nature and Grace, chapter 42 [XXXVI]; NPNF 1, Vol. V)
Augustine went a step farther. In an incidental remark against Pelagius, he agreed with him in excepting Mary, “propter honorem Domini,” from actual (but not from original) sin. This exception he is willing to make from the sinfulness of the race, but no other. He taught the sinless birth and life of Mary, but not her immaculate conception. . . . The reasoning of Augustine backward from the holiness of Christ to the holiness of His mother was an important turn, which was afterward pursued to further results. The same reasoning leads as easily to the doctrine of the immaculate conception of Mary, though also, just as well, to a sinless mother of Mary herself, and thus upward to the beginning, of the race, to another Eve who never fell.
(Schaff, HCC 3, 418-419)
We do not deliver Mary to the devil by the condition of her birth; but for this reason, because this very condition is resolved by the grace of rebirth. (Opus Imperf. Contra Julianum, 4, 122; Graef, 99)
And so he created a Virgin, whom he had chosen to be his Mother . . . she, with pious faith, merited to receive the holy seed within her. He chose her, to be created from her. (De peccatorum meritis et remissione, 2, 24, 38; Gambero, 219)