It is permissible to backbite non Muslims but it is not ethical. A Muslim is instructed to refrain from such acts even with non Muslims unless there is a need for that.

Backbiting is allowed when it is to warn someone of another to seek advice in a situation or to complain to the authority etc.

Is backbiting non muslims haram and wen is backbiting allowed?

Backbiting | February 12, 2014 11:14 am
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If for example we talk about a specific sect for example tablighi jamat and say they talk about FAZAIL AMAAL only will this be backbiting.. IS IT BACKBITIN IF WE DO NOT SPECIFY A PERSON BUT IF WE TALK IN GENERAL
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I saw a show about “the danger of the tongue” in which you said that is not permisible to label pleople… Does this count as gossip? If they label themselves, can we warn pleople against them?