Speaking ill of someone in their absence

Answer

Wa’alaykum as Salam wa rahmatullahi wa barakatuhu,

If there is a valid reason to disclose the faults of others, it will be permissible to disclose the same. Imam Nawawi (may Allah be pleased with him), has summarized the occasions when it is permissible to reveal the shortcomings of a person in the following text:

“Know that backbiting is permissible for valid reasons which are approved by Shari`ah. There are six reasons, which are as follows:

1. Oppression;
It is permissible for an oppressed person to reveal the oppression before the leader, judge, or anyone else in a similar position of authority so that his rights can be established. (This could be done) by saying, ‘A certain person has wronged me by doing such and such to me’,

2. Seeking aid (from a third person) to change a wrong and reform the sinner;
One can say to the person who can offer such assistance, “A certain person does these type of evil actions. can you exhort him?” etc. This is permissible as long as one intends to forbid evil. If one intends something else apart from this, then this act becomes unlawful,

3. Seeking a legal ruling;
In this case, one can say to the religious scholar: “My father/ brother/wife (for example) treated me unjustly. was it correct for him to behave in that way? How can my right be established?” etc. This will be fine only if need be. Then too, it is better to use word as: `What do you think of someone who did such and such?’ Here his objective of seeking a legal ruling is attained, without disclosing the fault of another. However, (although that is better) disclosing the name is permissible,

4. Warning other Muslims of the evil of a person and advising them, This could be done in various ways:
a) Criticizing weak narrators of Hadith. There is consensus that this is permissible , and in fact compulsory,
b) If someone asks advise about marrying, going into business partnership, dealing with a certain person, moving to stay next to a particular individual etc. In this case, it is compulsory upon the advisor to not hide anything. Rather, he should disclose the evils with the intention of giving good advice,
c) If a student is attending lessons of an innovator or a sinner and taking knowledge from them, and it is feared that this will affect and harm the student, then it is necessary to expose this to the student, with the intention of giving advice. Sometimes people talk about flaws of a teacher because of jealousy, and the devil makes him think that he is doing something good (therefore, he should insure that he has the correct intention),
d) If a person appointed to do something is unable to fulfill it, or he betrays the trust, or he is neglectful,then it will be necessary to inform the person who appointed such a person, so that he can remove him and appoint someone more capable, or atleast he can learn of his actions and not be deceived by him,

5) A person openly does wrong or innovates,
Like a person drinks wine openly etc. It is permissible to mention that particular sin openly (since he himself does it in public). It is not permissible to mention other sins of this person,

6) Identifying a person,
Like if a person is known for being blear-eyed, crippled, deaf, blind etc, it is permissible to identify them as such, and not use these terms in a derogatory manner. If he can describe such a person with other terms, it would be better.
These are six occasions when scholars mention that it is permissible to talk of the wrong of another person. There is consensus on most of these points.” (Riyaadh as-Saliheen, page 436)

The above text clearly answers all your queries