18 But who can fail to understand what they may be saying in their hearts? "What then are we to do," say they, "with those whom we have already rebaptized?" Return with them to the Church. Bring those whom you have wounded to be healed by the medicine of peace: bring those whom you have slain to be brought to life again by the life of charity. Brotherly union has great power in propitiating God. "If two of you," says our Lord, "shall agree on earth as touching anything that they shall ask, it shall be done for them." If for two men who agree, how much more for two communities?
Let us throw ourselves together on our knees before the Lord. Do you share with us our unity; let us share with you your contrition and let charity cover the multitude of sins. Seek counsel from the blessed Cyprian himself. See how much he considered to depend upon the blessing of unity, from which he did not sever himself to avoid the communion of those who disagreed with him; how, though he considered that those who were baptized outside the communion of the Church had no true baptism, he was yet willing to believe that, by simple admission into the Church, they might, merely in virtue of the bond of unity, be admitted to a share in pardon.
For thus he solved the question which he proposed to himself in writing as follows to Jubaianus: "But some will say, 'What then will become of those who, in times past, coming to the Church from heresy, were admitted without baptism?' The Lord is able of His mercy to grant pardon, and not to sever from the gifts of His Church those who, being out of simplicity admitted to the Church, have in the Church fallen asleep."
Source: On Baptism, Against the Donatists (New Advent)