121 Petilianus said: "If you make prayer to God, or utter supplication, it profits you absolutely nothing whatsoever. For your blood-stained conscience makes your feeble prayers of no effect; because the Lord God regards purity of conscience more than the words of supplication, according to the saying of the Lord Christ, ‘Not every one that says unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that does the will of my Father which is in heaven.' The will of God unquestionably is good, for therefore we pray as follows in the holy prayer, ‘Your will be done in earth, as it is in heaven,' that, as His will is good, so it may confer on us whatever may be good. You therefore do not do the will of God, because you do what is evil every day."
122. Augustine answered: If we on our side were to utter against you all that you assert against us, would not any one who heard us consider that we were rather insane litigants than Christian disputants, if he himself were in his senses? We do not, therefore, render for railing. For it is not fitting that the servant of the Lord should strive; but he should be gentle unto all men, willing to learn, in meekness instructing those that oppose themselves. If, therefore, we reproach you with those who daily do what is evil among you, we are guilty of striving unbefittingly, accusing one for the sins of another. But if we admonish you, that as you are unwilling that these things should be brought against yourselves, so you should abstain from bringing against us the sins of other men, we then in meekness are instructing you, solely in the hope that some time you will return to a better mind.
Source: Answer to Letters of Petilian, Bishop of Cirta (New Advent)