Backbiting is permissible only for valid reasons approved by Shari'ah. These reasons are as follows:
1- It is permissible for an oppressed person to speak before the judge or someone in a similar position of authority to help him or her establish his or her rights by telling him 'so-and-so wronged me and has done such and such to me' etc.
2- It is permissible to seek somebody's assistance in forbidding evil and helping someone change his or her immoral conduct. One can say to the person who can offer such assistance, 'so-and-so does such and such evil deeds. Can you exhort him?' etc. This is permissible as long as one intends to forbid evil. If, however, one intends something else apart from this, then this act becomes unlawful.
3- One who seeks legal verdict on a certain matter may point out the defaults of another person or relate something else. One in this case can say to the Mufti (religious scholar who issues verdicts): "My father or brother (for example) treated me unjustly. Can I get my right established?" etc. This is permissible to say only if need be, but it is better to say 'What do you think of someone who did such and such?' This does not mean, however, that naming the person in question is not permissible, Hadith No. 1535 makes this point clear.
4- One who criticizes those who openly commit acts of disobedience, such as drinking wine, gambling, engaging in immoral habits, fornication, hypocrisy, and making mischief.
5- It is permissible to call into question the narrators of Hadith, and witnesses in the court when the need arises. It is also permissible to mention the bad qualities of somebody for marriage purposes in case an advice is sought. Also, if one has noticed that a "seeker of knowledge" frequently goes to the gatherings of an innovator in religion and one fears that this "seeker of knowledge" may be affected by this so-called scholar, then he must in this case give counsel to the "seeker of knowledge" by telling him about the "innovator," etc.
6- It is permissible to use names such as "Al-a'mash" which means 'the blear-eyed' to talk about people who are known by such names for the sake of identification and not for disparaging people and underestimating them. To identify them without resorting to such names is however better.
1531. 'Aishah (May Allah be pleased with her) said: A man sought permission for audience with the Prophet (PBUH). He said, "Give him permission but he is a bad member of his tribe."