47 Petilianus said: "Accordingly, as we have said, the Lord Christ cried, ‘Saul, Saul, why do you persecute me? It is hard for you to kick against the pricks. And he said, Who are You, Lord? And the Lord said, I am Christ of Nazareth, whom you persecute. And he, trembling and astonished, said, Lord, what will You have me to do? And the Lord said unto him, Arise, and go into the city, and it shall be told you what you must do.' And so presently it goes on, ‘But Saul arose from the earth; and when his eyes were opened, he saw no man.' See here how blindness, coming in punishment of madness, obscures the light in the eyes of the persecutor, not to be again expelled except by baptism! Let us see, therefore, what he did in the city. ‘Ananias,' it is said, ‘entered into the house to Saul, and putting his hands on him, said, Brother Saul, the Lord, even Jesus, that appeared unto you in the way as you came, has sent me, that you might receive your sight, and be filled with the Holy Ghost. And immediately there fell from his eyes as it had been scales; and he received sight immediately, and arose, and was baptized.' Seeing therefore that Paul, being freed by baptism from the offense of persecution, received again his eyesight freed from guilt, why will not you, a persecutor and traditor, blinded by false baptism be baptized by those whom you persecute?"
48. Augustine answered: You do not prove that I, whom you wish to baptize afresh, am either a persecutor or a traditor. And if you prove this charge against any one, yet the persecutor and traditor is not to be baptized afresh, if he had been baptized already with the baptism of Christ. For the reason why it was necessary that Paul should be baptized was that he had never been washed in any baptism of the kind. Therefore what you have chosen to insert about Paul has no point of resemblance with the case which you are arguing with us. But if you had not inserted this, you would have found no place for your childish declamation, "See how blindness comes in punishment of madness, not to be again expelled except by baptism!" For with how much more force might one exclaim against you, See how blindness comes in punishment of madness, which, finding its similitude in Simon, not in Paul, is not expelled from you even when you have received baptism? For if persecutors ought to be baptized by those whom they persecute, then let Primianus be baptized by the followers of Maximianus, whom he persecuted with the utmost eagerness.
Source: Answer to Letters of Petilian, Bishop of Cirta (New Advent)