21 What then, say they, will become of those who, coming from the heretics, have been received without the baptism of the Church? If they have departed this life, they are reckoned in the number of those who have been catechumens indeed among us, but have died before they were baptized—no trifling advantage of truth and faith, to which they had attained by forsaking error, although, being prevented by death, they had not gained the consummation of grace. But they who still abide in life should be baptized with the baptism of the Church, that they may obtain remission of sins, lest by the presumption of others they remain in their old error, and die without the completion of grace. But what a crime is theirs on the one hand who receive, or on the other, theirs who are received, that their foulness not being washed away by the layer of the Church, nor their sins put away, communion being rashly seized, they touch the body and blood of the Lord, although it is written, “Whosoever shall eat the bread or drink the cup of the Lord unworthily, shall be guilty of the body and blood of the Lord!”
Source: The Epistles of Cyprian (New Advent)