Is it permissible to mention the wicked person with what is in him to warn against him while he is absent?

It is permissible to mention the transgressor (fasiq) with what is in him for the purpose of warning against him, and this may even be obligatory. The general rule regarding backbiting (gheeba) is its prohibition, but it may become obligatory or permissible for a legitimate Sharia purpose that cannot be achieved except through it. Among these situations is warning Muslims against evil, such as discrediting narrators, witnesses, and those who undertake issuing fatwas or teaching while lacking qualification, or due to their transgression or innovation. The same applies to one who openly declares his transgression or innovation; it is permissible to mention them only with what they have openly declared.