What is the authenticity of the report: “There is no backbiting of an open sinner”? And when is backbiting permissible?

Question:
In whose case is backbiting permissible? And is the hadith: authentic?

Answer:
The hadith is not authentic, as far as I know. However, the scholars mentioned six things in which backbiting is permissible: when one displays open sinfulness, and so on in seeking a legal ruling, and so on in complaining of injustice, and so on in criticizing witnesses, and criticizing narrators. All these matters are permissible, and so on in giving sincere advice; when someone seeks your advice and consults you. These six matters do not involve backbiting: when criticizing witnesses, when criticizing narrators, when the one seeking a ruling asks you about such and such: a woman asks you for a ruling on taking from her husband’s wealth because he is stingy and does not give her her rights, or asks you about a person who wronged her: should she sue him? Should she take from his wealth in exchange for her right? And the like of that.
So if a person displays open sinfulness, there is no backbiting regarding him: if he displays shaving the beard, and a person says, "This so-and-so has shaved his beard," it is not backbiting. And if he lets his garments hang below the ankles, and some people say about him that he is one who lets his garments hang, it is not backbiting; because he displayed it. He is the one who displayed the sin, he is the one who exposed himself, so he is not called one who is backbitten—may Allah keep us safe.