Must avoid sinners and heretics

"It is an illusion to seek the company of sinners on the pretence of reforming them or of converting them; it is far more to be feared that they will spread their poison to us." - St. Gregory Nazianzen

"So great is my aversion for the company of heretics, or of conversation with them, that I say we ought not even go near them." - St. Anthony the Abbot

"St. Anthony the Abbot would not speak to a heretic, except to exhort him to the true faith; and he drove all heretics from his mountain, calling them venomous serpents." - St. Athanasius

"I entreat you to shun, whenever possible, the society of those who profess false doctrines." - St. John Eudes

If anyone walks according to a foreign doctrine, he is not of Christ nor a partaker of His passion. Have no fellowship with such a man, lest you perish along with him, even though he should be your father, your son, your brother, or a member of your family. St. Ignatius of Antioch

"These men are Protestants; they are heretics! Have nothing to do with them!" - St. Anthony Mary Claret (Anthony Mary: THE MODERN APOSTLE, Claretian Missionaries, Dominguez Seminary, Compton, CA: 1934, p.28)

Taken from Apologetic Digest (use interlibrary loan) by Michale Malone.