92 Natalis of Oëa said: "It is not only I myself who am present, but also Pompeius of Sabrati, and Dioga of Leptis Magna, who commissioned me to represent their views, being absent indeed in body, but present in spirit, who deliver this same judgment as our colleagues, that heretics cannot have communion with us, unless they have been baptized with the baptism of the Church."
93. He means, I suppose, that communion which belongs to the society of the Dove; for in the partaking of the sacraments they doubtless held communion with them, judging no man, nor removing any from the right of communion if he held a different opinion. But with whatever reference he spoke, there is no great need for these words being refuted. For certainly a heretic would not be admitted to communion, unless he had been baptized with the baptism of the Church. But it is clear that the baptism of the Church exists even among heretics if it be consecrated with the words of the gospel; just as the gospel itself belongs to the Church, and has nothing to do with their waywardness, but certainly retains its own holiness.
Source: On Baptism, Against the Donatists (New Advent)