43 Standing firm then in your hearts, drive away from the Church the wolves which seek to carry off prey. Let there be no sloth in you, let not your mouth be evil nor your tongue bitter. Do not sit in the council of vanity; for it is written, “I have not sat in the council of vanity.” Do not listen to those who speak against their neighbours, lest while you listen to others, you be stirred up yourselves to speak against your neighbours, and it be said to each of you: “You sat and spoke against your brother.”
Source: Letters (New Advent)