Lesson III: Withdraw from backbiters' deadly conversations.
Freeze their tongue with a sudden departure, so at least they know that you disapprove of such language. That is Saint Jerome's advice: "If you hear someone speaking ill of another, cast him far from you like a serpent; so that, overcome by shame, he will learn to be silent regarding the actions of others." (13) He learned this from Saint Paul, who says, "I write to you not to associate with one who is called a brother, if he is immoral, or covetous, or an idolater or evil-tongued." (14)
(13) Saint Jerome, In Reg. Mon, Chapter 22
(14) I Cor 5:11
Cassian relates having seen an elder called Machetus who had obtained a very singular grace from God: as long as people were talking about the things of God he would not feel sleepy, even if the conversation lasted night and day; but if, on the contrary, people were speaking useless words or beginning to backbite their neighbor, he would fall asleep at once.
Those who do not want to imitate this elder, who cannot fall asleep or do not want to, should at least show that they are Christians by indicating their displeasure with some sign. They should do this right at the start of the conversation, when a bucket of water will suffice to put the fire out. For you will have a hard time mastering the fire once it has become a conflagration. "The north wind drives away rain, as does a sad countenance a backbiting tongue." (15) And Saint Jerome adds, "if you listen to a backbiter with a happy look you encourage him to continue backbiting; he shakes the coals, and then you add the wood. If, on the contrary, you listen to him with a sad, unhappy look he will learn to spare his words when he sees that you are not listening to him willingly. If you do not do this, you show that you are a false brother of the one who is backbiting, or that you are a cowardly friend."
(15) Prov 25:23
V.
My friends, by acting otherwise -- by showing less care for others' reputation than for our own -- we violate the law of Our Lord, who tells us to love our neighbor as ourself. The person who sets fire to his neighbor's house is sinful, but so is the man who warms himself by the heat of the burning house. If he is not an enemy, then let him carry some water to put out the fire. In the same way, we do harm not only by backbiting others, but also by not stopping those who backbite, encouraging them with praise and applause. A sincere friend not only avoids backbiting, but also does everything he can to bring it to a halt. A devoted brother hides his brother's dishonorable vices from others, revealing them only to those who are able to remedy them.

Apelles depicted King Antigone as a person with only one eye. However, he also disposed the king's portrait at an angle whereby his physical defects might be attributed to the painting, showing only that part of his face which could not be seen to disadvantage. (16)
(16) Phil., Hist. Nat. lib, Book 35, Chapter 10

Such are the portraits drawn by a truly Christian hand. It neglects anything vicious in the face of another and shows only whatever is worthy of being seen.
Plato imitated Apelles perfectly, not by hand or brush, but by his care in hiding the vices of others. Someone came to inform him that his disciple Xenocrates had been telling all sorts of malicious stories about him. Plato, careful to avoid believing this badly motivated report, replied, "It is highly improbable." Since the accuser insisted with every appearance of truth, Plato added, "I cannot believe that I am not loved by someone I love so much." It availed nothing for the accuser to swear that what he said was true. Not wanting to test whether the man was lying, Plato simply said, "Xenocrates would not have spoken thus unless he thought he were doing me a favor." (17)
(17) Valer., Book 4, Chapter 1.
That is how we should attenuate and cover the vices of others, instead of exaggerating and proclaiming them everywhere. Solomon advises us, "Do not give heed to every word that is spoken." (18) And Saint Bernard confirms what he wrote on this subject by saying, "Backbiters pour poison into the ears of those who listen to them." (19) Both the backbiter and his complacent listener commit sin. If a man with a perfidious tongue advises someone to swallow poison, that person will die. The backbiter furtively robs you of the virtue of charity, and he makes your fraternal love grow cold without your even being aware of it.
(18) Eccl 7:22
(19) Saint Bernard, De modo bene vivendi, Chapters 17 and 37; Serm. De Tripl.