74 Felix of Gurgites said: "I give my judgment, that, according to the precepts of the holy Scriptures, those who have been unlawfully baptized outside the Church by heretics, if they wish to flee to the Church, should obtain the grace of baptism where it is lawfully given."
75. Our answer is: Let them indeed begin to have in a lawful manner to salvation what they before had unlawfully to destruction; because each man is justified under the same baptism, when he has turned himself to God with a true heart, as that under which he was condemned, when on receiving it he "renounced the world in words alone, and not in deeds."
Source: On Baptism, Against the Donatists (New Advent)