22 Lucius of Castra Galbæ said: "Since the Lord has said in His gospel, 'You are the salt of the earth: but if the salt have lost his savor, that which is salted from it shall be thenceforth good for nothing, but to be cast out, and to be trodden under foot of men.' and seeing that again, after His resurrection, when sending forth His apostles, He commanded them, saying, 'All power is given unto me in heaven and in earth: go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost,' — since then it is plain that heretics, that is, the enemies of Christ, have not the full confession of the sacrament, also that schismatics cannot reason with spiritual wisdom, since they themselves, by withdrawing when they have lost their savor from the Church, which is one, have become contrary to it, let that be done which is written, 'The houses of those that are opposed to the law must needs be cleansed.' and it therefore follows that those who have been polluted by being baptized by men opposed to Christ should first be cleansed, and only then baptized."
23. Lucius of Castra Galbæ has brought forward a proof from the gospel, in the words of the Lord, "You are the salt of the earth: but if the salt have lost his savor, that which is salted from it shall be good for nothing, but to be cast out, and to be trodden under foot of men;" just as though we maintained that men when cast out were of any profit for the salvation either of themselves or of any one else. But those also who, though seeming to be within, are yet of such a kind, not only are without spiritually, but will in the end be separated in the body also. For all such are for nothing. But it does not therefore follow that the sacrament of baptism which is in them is nothing. For even in the very men who are cast out, if they return to their senses and come back, the salvation which had departed from them returns; but the baptism does not return, because it never had departed. And in what the Lord says, "Go therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost," He did not permit any to baptize except the good, inasmuch as He did not say to the bad, "Whosesoever sins ye remit, they are remitted unto them; and whosesoever sins ye retain, they are retained." How then do the wicked baptize within, who cannot remit sins? How also is it that they baptize the wicked whose hearts are not changed, whose sins are yet upon them, as John says, "He that hates his brother is in darkness even until now?" But if the sins of these men are remitted when they join themselves in the close bonds of love to the good and just, through whom sins are remitted in the Church, though they have been baptized by the wicked, so the sins of those also are remitted who come from without and join themselves by the inner bond of peace to the same framework of the body of Christ. Yet the baptism of Christ should be acknowledged in both, and held invalid in none, whether before they are converted, though then it profit them nothing, or after they are converted, that so it may profit them, as he says, "Since they themselves, by withdrawing when they have lost their savor from the Church, which is one, have become contrary to it, let that be done which is written, 'The houses of those that are opposed to the law must need be cleansed.' And it therefore follows," he goes on to say, "that those who have been polluted by being baptized by men opposed to Christ should first be cleansed, and only then baptized." What then? Are thieves and murderers not contrary to the law, which says, "You shall not kill; you shall not steal?" "They must therefore needs be cleansed." Who will deny it? And yet not only those who are baptized by such within the Church, but also those who, being such themselves, are baptized without being changed in heart, are nevertheless exempt from further baptism when they are so changed. So great is the force of the sacrament of mere baptism, that though we allow that a man who has been baptized and continues to lead an evil life requires to be cleansed, we yet forbid him to be any more baptized.
Source: On Baptism, Against the Donatists (New Advent)