But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolator, or a railer, or a drunkard, or an extortioner; with such an one no not to eat. For what have I to do to judge them also that are without? Do not ye judge them that are within? But them that are without God judgeth. Therefore put away from among yourselves that wicked person. 1 Corinthians 5:11-13

Of whom is Hymenaeus and Alexander; whom I have delivered unto Satan, that they may learn not to blaspheme. 1 Timothy 1:20

And reprove one another, not in anger, but in peace, as you have it in the Gospel. But to anyone that acts amiss against another, let no one speak, nor let him hear anything from you until he repents. Didache (A.D. 80-140) ch.15

All of those who separate from the church and give heed to old wives’ tales, like these persons, are truly self-condemned. Paul commands us “to avoid [these men] after a first and second admonition.” Furthermore, John, the disciple of the Lord, has intensified their condemnation. For he desires us not even to address them with the salutation of “Godspeed.” He says, “He who bids them Godspeed is a partaker with their evil deeds.” Irenaeus (A.D. 180) Ante-Nicene Fathers vol.1 pg. 341, 342

“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 you therefore partakers with them.” Therefore let no one associate himself with the contumacious, and those who do not fear God, and those who entirely withdraw 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. Cyprian (A.D. 250) Ante-Nicene Fathers vol.5 pg.365

From all such persons, therefore, it behooves us to keep aloof, but to adhere to those who, as I have already observed, do hold the doctrine of the apostles, and who, together with the order of priesthood (presbyterii ordine), display sound speech and blameless conduct for the confirmation and correction of others. Irenaeus (A.D. 180) Ante-Nicene Fathers vol.1 pg. 497

Now, reproof addressed to sinners has their salvation for its aim, the word being harmoniously adjusted to each one's conduct; now with tightened, now with relaxed cords. Clement of Alexandria (A.D. 195) Ante-Nicene Fathers vol.2 pg.226

But it will be said that some of us, too, depart from the rules of our discipline. In that case, however, we count such persons no longer as Christians. Tertullian (A.D. 198) Ante-Nicene Fathers vol.3 pg.51

[ADDRESSED TO PAGANS:] Persons of this doubtful mold do not assemble with us. Neither do they belong to our communion. By their delinquency, they become yours once more. For we are unwilling to mix even with those whom your violence and cruelty have compelled to recant. Yet, we should, of course, be more ready to have included among us those who have unwillingly forsaken our discipline, than willful apostates. However, you have no right to call them Christians to whom Christians themselves deny that name. Tertullian (A.D. 198) Ante-Nicene Fathers vol.3 pg.113

What would be said, if, when you thought the doctor necessary, you were to find fault with his instruments, because they cut, or cauterize, or amputate, or tighten; whereas there could be no doctor of any value without his professional tools? Censure, if you please, the practitioner who cuts badly, amputates clumsily, is rash in his surgery; and even blame his implements as rough tools of his are. Your conduct is equally unreasonable, when you allow indeed that God is a judge, but at the same time destroy those operations and dispositions by which He discharges His judicial functions. We are taught God by the prophets, and by Christ, not by the philosophers nor by Epicurus. Tertullian (A.D. 198) Ante-Nicene Fathers vol.3 pg. 309

In this example of a leper … [the Law] prohibited any contact with a person who was defiled with sin. The apostle also forbids us even to eat food with such a one. For the taint of sins can be communicated as if contagious, wherever a man mixes himself with the sinner. Tertullian (A.D. 198) Ante-Nicene Fathers vol.3 pg. 355

We must separate from a believer who lives irregularly and contrary to discipline. Paul [said] to the Thessalonians: “But we have commanded you, in the name of Jesus Christ, that you depart from all brethren who walk disorderly and not according to the tradition that you have received from us.” Cyprian (A.D. 250) Ante-Nicene Fathers vol.5 pg. 551