36 Theogenes of Hippo Regius said: "According to the sacrament of the heavenly grace of God which we have received, we believe in the one only baptism which is in the holy Church."
37. This may be my own judgment also. For it is so balanced, that it contains nothing contrary to the truth. For we also believe in the one only baptism which is in the holy Church. Had he said, indeed, We believe in that which is in the holy Church alone, the same answer must have been made to him as to the rest. But as it is, since he has expressed himself in this wise, "We believe in the one only baptism which is in the holy Church," so that it is asserted that it exists in the holy Church, but not denied that it may be elsewhere as well, whatever his meaning may have been, there is no need to argue against these words. For if I were questioned on the several points, first, whether there was one baptism, I should answer that there was one. Then if I were asked, whether this was in the holy Church, I should answer that it was. In the third place, if it were asked whether I believed in this baptism, I should answer that I did so believe; and consequently I should answer that I believed in the one baptism which is in the holy Church. But if it were asked whether it was found in the holy Church alone, and not among heretics and schismatics, I should answer that, in common with the whole Church, I believed the contrary. But since he did not insert this in his judgment, I should consider that it was mere wantonness if I added words which I did not find there, for the sake of arguing against them. For if he were to say, There is one water of the river Euphrates, which is in Paradise, no one could gainsay the truth of what he said. But if he were asked whether that water were in Paradise and nowhere else, and were to say that this was so, he would be saying what was false. For, besides Paradise, it is also in those lands into which it flows from that source. But who is rash enough to say that he would have been likely to assert what is false, when it is quite possible that he was asserting what is true? Wherefore the words of this judgment require no contradiction, because they in no wise run counter to the truth.
Source: On Baptism, Against the Donatists (New Advent)