To Florus 3.160
Yet the man slain by the thunderbolt of such clear truth seems still to breathe in some respect when compared with you. His whole doctrinal structure collapses when only its foundation gives way. But three things in your case totter as his one does. Consider, then, whether any part of your building can rise.
Mani thought sin natural, though it can only be voluntary, and so laid his foundations in empty space. The rest he placed consistently alongside: since sin is natural, nature is evil; an evil thing cannot have a good author; therefore the whole human race must be attributed to the prince of darkness. All this could have stood, had truth not undermined his first claim: sin, a work of free will, cannot be shown natural, and whatever is natural cannot be sin.
Latin
Sed tamen ille, qui fulmine tam perspicuae veritatis interiit, ex parte aliqua videtur spirare, cum confertur tibi; illi enim tota dogmatis sui fundamento eius tantummodo nutante structura collabitur, tibi autem tria similiter vacillant ut illi unum. Ac per hoc vide, utrum aedificii tui quidquam possit assurgere. Mani ergo putans naturale esse peccatum, quod nisi voluntarium esse non potest, in vacuo fundamenta locavit; reliqua vero iuxta se consequenter imposuit dicens, quoniam est naturale peccatum, malam esse naturam, malae autem rei auctorem bonum non esse ac per hoc omne humanum genus reputandum principi tenebrarum. Quod totum utique stare potuisset, nisi illud primum eius suffodisset veritas, id est peccatum opus liberae voluntatis doceri naturale non posse et, quidquid fuisset naturale, peccatum esse non posse.