“Backbite, calumny, slander; forbidden
Cursing too and leaking secrets hidden
Lewdness, vulgarity, harm, and deceit
Mockery, ridicule, lying discreet!”
In those works, backbiting, in general, is considered a terrible sin with very few exceptions. All means should be exhausted to avoid backbiting others be they Muslim or of another faith unless it is justified e.g. warning others of harm, seeking counsel, etc.
Allah knows best.Source: al-Adab al-Shar’iyyah
This answer was collected from HanbaliDisciples.com. The questions have been answered by Imam John Starling.