Qatadah said concerning this verse: "Why, when you heard it" [Surah An-Nur: 12]: you should have rejected it and said that this is a clear lie. By my life! When you hear something bad about your Muslim brother, not to tell a lie against him is better for you, and safer, than spreading it, publicising it and believing it.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19492