Nicene and Post-Nicene Fathers, Vol. IV:
Writings in Connection with the Donatist Controversy.: Chapter 3

Chapter 3.—6.  Petilianus said:  "For what we look to is the conscience of the giver, to cleanse that of the recipient."

7.  Augustin answered:  We therefore need have no anxiety about the conscience of Christ.  But if you assert any man to be the giver, be he who he may, there will be no p. 531 certainty about the cleansing of the recipient, because there is no certainty about the conscience of the giver.