5 Let the lapsed, however, who acknowledge the greatness of their sin, not depart from entreating the Lord, nor forsake the Catholic Church, which has been appointed one and alone by the Lord; but, continuing in their atonements and entreating the Lord's mercy, let them knock at the door of the Church, that they may be received there where once they were, and may return to Christ from whom they have departed, and not listen to those who deceive them with a fallacious and deadly seduction; since it is written, “Let no man deceive you with vain words, for because of these things comes the wrath of God upon the children of disobedience; be not therefore partakers with them.” Therefore let no one associate himself with the contumacious, and those who do not fear God, and those who entirely with draw from the Church.
But if any one should be impatient of entreating the Lord who is offended, and should be unwilling to obey us, but should follow desperate and abandoned men, he must take the blame to himself when the day of judgment shall come. For how shall he be able in that day to entreat the Lord, who has both before this denied Christ, and now also the Church of Christ, and not obeying bishops sound and wholesome and living, has made himself an associate and a partaker with the dying? I bid you, dearest brethren and longed-for, ever heartily farewell.
Source: The Epistles of Cyprian (New Advent)