Speak not evil of thy brother, even if thou seest him transgressing all the commandments. Otherwise, thou thyself wilt fall into the hands of thine enemies.
Venerable Anthony the Great
A proud and evil word directs even good men toward evil, while a humble and good word turns even the evil toward good.
Abba Agathon, when he would see some bad deed and his thought would urge him to condemnation, would say to himself: "Agathon! See that thou not do this thyself! - and his thought would calm down.
St. Macarius the Great
Because of the words of the serpent, Eve was expelled from paradise - such also is speaking evil of one's neighbor. It destroys the hearer and destroys also the soul of the speaker.
Abba Agathon
It is better to eat meat and drink wine, than to devour thy brother through speaking evil.
Abba Hyperechius
If in thy presence a brother calumniates a brother, do not thou also say: "Yes, it is so"; but either keep silent, or say: "Brother! I myself am sinful and cannot judge another'. Thus, thou wilt save from condemnation both thyself and the soul of him who is speaking with thee.
From "The Life of the Elders"