8 All therefore speak falsely who disallow his (Adam's) salvation, shutting themselves out from life for ever, in that they do not believe that the sheep which had perished has been found. For if it has not been found, the whole human race is still held in a state of perdition. False, therefore, is that, man who first started this idea, or rather, this ignorance and blindness— Tatian. As I have already indicated, this man entangled himself with all the heretics. This dogma, however, has been invented by himself, in order that, by introducing something new, independently of the rest, and by speaking vanity, he might acquire for himself hearers void of faith, affecting to be esteemed a teacher, and endeavouring from time to time to employ sayings of this kind often [made use of] by Paul: “In Adam we all die;” ignorant, however, that “where sin abounded, grace did much more abound.” Since this, then, has been clearly shown, let all his disciples be put to shame, and let them wrangle about Adam, as if some great gain were to accrue to them if he be not saved; when they profit nothing more [by that], even as the serpent also did not profit when persuading man [to sin], except to this effect, that he proved him a transgressor, obtaining man as the first-fruits of his own apostasy. But he did not know God's power. Thus also do those who disallow Adam's salvation gain nothing, except this, that they render themselves heretics and apostates from the truth, and show themselves patrons of the serpent and of death.
Source: Adversus haereses (New Advent)