Know that in the same way that backbiting is forbidden for the one who speaks it, it is likewise forbidden for the one who listens to it and approves of it.
Thus, it is obligatory on the one who hears an individual embarking on committing the prohibited form of backbiting, to forbid him from doing it as long as he does not fear any open harm resulting from that. But if he does fear (harm) from that, then he is obligated to reject the backbiting with his heart and to detach himself from that gathering if he is able to do so. If he has the ability to reject it with his tongue or to cut the backbiting off by changing the topic, then that becomes required of him. And if he does not do that, then he has committed an act of disobedience (i.e. sinned).
If he is forced to stay in that gathering in which backbiting is taking place, and he fears from forbidding it, or he forbids it but it is not accepted from him and he cannot find a way to separate himself from them, then he is prohibited from listening and paying attention to the backbiting. Instead, his way out should be by making remembrance of Allaah (dhikr) with both his tongue and heart or just his heart. Or he should think about something else in order to preoccupy himself from having to listen to it. After having done this, his hearing it without listening or paying attention to it will not harm him, while he is in this mentioned state. If he is able, after this, to withdraw from them and they are still backbiting, then separating oneself is an obligation. Allaah says:
“And when you see those who engage in false conversations about Our verses by mocking at them, then turn away from them until they engage in a different topic of speech. But if the Devil causes you to forget, then after remembering, do not sit in the company of those people who are the wrong-doers.” [Surah AlAn’aam: 68]
It has been reported that Ibraaheem bin Adham was once invited to a waleemah (wedding feast), so he attended it and found people there who were mentioning a man that didn’t come, saying: “He is truly lazy.” So Ibraaheem said: “I brought this upon myself, such that I attended a place in which people are backbiting one another.” So he left from there and did not eat for three days. What has been recited of poetry with regard to this is:
“And restrain your ears from hearing vile speech
Just as you restrain your tongue from speaking it
Because when you listen to this vile speech
You are a partner to the one saying it, so reflect.”
What Should One Do When He Hears His Shaikh, Friend Or Someone Else Being Backbitten?
Know that it is upon the one who hears a Muslim being backbitten to oppose it and prevent the one doing the backbiting. If he is not able to prevent him with his speech, then he should stop him with his hand. If he is neither able to do so with his hand or with his tongue, then he should get up and leave that gathering. And if he hears his teacher (shaikh) being backbitten – or anyone else who has a right over him, or if the person (being backbitten) is from the people of righteousness and nobility, then his concern with what we have mentioned above should be greater.
Posted From the e-Book : Guarding the Tongue – Imaam An-Nawawee