Detraction Or Speaking Injuriously Of Another Is Forbidden

The brothers are to speak evil of none (Titus 3:2); there must be no complaining, no slander; it is written, "Whisperers and detractors are people hateful to God" (Romans 1:29). And let them be moderate, showing all mildness to all men (Titus 3:2), without word of criticism or condemnation; as the Lord says, they must give no thought even to the slightest faults of others (Matthew 7:3; Luke 6:41), but rather count over their own in the bitterness of their soul (Isiah 38:15).

Saint Francis of Assisi
Rule of 1221
Chapter 11