36 Petilianus said: "The Lord Christ also warns us, saying, ‘Beware of false prophets, which come unto you in sheep's clothing, but inwardly they are ravening wolves; and you shall not know them by their fruits.'"
37. Augustine answered: If I were to inquire of you by what fruits you know us to be ravening wolves, you are sure to answer by charging us with the sins of other men, and these such as were never proved against those who are said to have been guilty of them. But if you should ask of me by what fruits we know you rather to be ravening wolves, I bring against you the charge of schism, which you will deny, but which I will straightway go on to prove; for, as a matter of fact, you do not communicate with all the nations of the earth, nor with those Churches which were founded by the labor of the apostles. Hereupon you will say, "I do not communicate with traditors and murderers." The seed of Abraham answers you, "These are those charges which you made, which are either not true, or have no reference to me." But these I set aside for the present; do you meanwhile show me the Church. Now that voice will sound in my ears which the Lord showed was to be avoided in the false prophets who made a show of their several parties, and strove to estrange men from the Catholic Church, "Lo, here is Christ, or there." But do you think that the true sheep of Christ are so utterly destitute of sense, who are told, "Believe it not," that they will hearken to the wolf when he says, "Lo, here is Christ," and will not hearken to the Shepherd when He says, "Throughout all nations, beginning at Jerusalem?"
Source: Answer to Letters of Petilian, Bishop of Cirta (New Advent)