188 Petilianus said: "Is it then the case that God has ordered the massacre even of schismatics? And if He were to issue such an order at all, you ought to be slain by some barbarians and Scythians, not by Christians."
189. Augustine answered: Let your Circumcelliones remain quiet, and let me entreat you not to terrify us about barbarians. But as to whether we or you are schismatics, let the question be put neither to you nor to me, but to Christ, that He may show where His Church is to be found. Read the gospel then, and there you find the answer, "In Jerusalem, and in all Judea, and in Samaria and even in the whole earth." If any one, therefore, is not found within the Church, let not any further question be put to him, but let him either be corrected or converted, or else, being detected, let him not complain.
Source: Answer to Letters of Petilian, Bishop of Cirta (New Advent)