Answered by Shaykh Abu Usamah
If a person sees a young woman she knows doing something haram with another boy (right infront of her eyes), does she have to tell the girl’s parents? Should she say nothing because she was the only one who saw?
Answer:
Al-Salam alaykum
In such a case it is necessary that she fulfils her responsibility of stopping evil by doing what is in her capacity i.e. telling those who will be able to effect some reform viz. the girl’s parents. This will not be regarded as ghibah (backbiting) as the intention is to reform.
[Faraz adds: Imam Abu’l Layth al-Samarqandi mentioned that things said out of genuine concern are not backbiting (ghiba), as in Sharhal-Tariqa al-Muhammadiyya and elsewhere.]