Among the most undesirable kinds of idle talk must also be included everything that is said about others.
Unless you are responsible for certain people, as a guardian, a teacher or a departmental head, what others do or do not do is no concern of yours and you must refrain from talking about them, from giving your opinion about them and what they do, and from repeating what others may think or say about them.
It may happen that the very nature of your occupation makes it your duty to report what is taking place in a particular department, undertaking or communal work. But then the report should be confined to the work alone and not touch upon private matters. And as an absolute rule, it must be wholly objective. You should not allow any personal reaction, any preference, any like or dislike to creep in. And above all, never introduce your own petty personal grudges into the work that is assigned to you.
In all cases and as a general rule, the less one speaks of others, even to praise them, the better. It is already so difficult to know exactly what is happening in oneself—how can one know with certainty what is happening in others? So you must totally abstain from pronouncing upon anybody one of those final judgments which cannot but be foolish if not spiteful.
Ref : On Education