9 When therefore we teach ours to blaspheme God that the Priscillianists may believe them theirs, let us see what evil themselves say when they therefore lie that we may believe them ours. They anathematize Priscillian, and detest him according to our mind; they say that the soul is a creature of God, not a part; they execrate the Priscillianists' false martyrdoms; the catholic bishops by whom that heresy has been stripped, attacked, prostrated, they extol with great praises, and so forth.
Behold, themselves speak truth when they lie: not that the very thing which is a lie can be true at the same time; but when in one thing they lie, in another they speak truth: for when, in saying they are of us, they lie, of the catholic faith they speak truth. And therefore they, that they may not be found out for Priscillianists, speak in lying manner the truth: but we, that we may find them out, not only speak lyingly, that we may be believed to belong to them; but we also speak false things which we know to belong to their error.
Therefore as for them, when they wish to be thought of us, it is both false in part, and true in part, what they say; for it is false that they are of us, but true that the soul is not a part of God: but as for us, when we wish to be thought to belong to them, it is false, both the one and the other that we say, both that we are Priscillianists, and that the soul is a part of God. They, then, praise God, not blaspheme, when they conceal themselves; and when they do not so, but utter their own sentiments, they know not that they blaspheme.
So that if they be converted to the catholic faith, they console themselves, because they can say what the Apostle said: who when among other things he had said, “I was before a blasphemer; but,” says he, “I obtained mercy, because I did it ignorantly.” We on the contrary, in order that they may open themselves to us, if we utter this as if it were a just lie for deceiving and catching them, do assuredly both say that we belong to the blaspheming Priscillianists, and that they may believe us, do without excuse of ignorance blaspheme. For a catholic, who by blaspheming wishes to be thought a heretic, cannot say, “I did it ignorantly.”
Source: To Consentius: Against Lying (New Advent)