What is the expiation for backbiting someone whom it is difficult to inform, or who is not worthy of being mentioned? And is silence in gatherings where there is backbiting, or not forbidding the backbiter when there is embarrassment, considered participation in backbiting?

The repentance of someone who has backbitten involves remorse, refraining from the act, and resolving never to return to it, along with supplicating and seeking forgiveness for the person they backbit, without informing them, because informing them might cause harm. It is not obligatory to mention their good qualities. As for sitting in a gathering where backbiting occurs, it is not permissible to remain silent about backbiting. The listener must denounce it with their tongue or their heart, and leave the gathering if the backbiting does not cease, unless there is a necessity or an inability to denounce and leave. In such a case, one should occupy themselves with the remembrance of Allah or thinking about something else, and hearing it will not harm them then.