´It was narrated from Sufyan bin Zubaid, from Abu Wa'il, from 'Abdullah:` "The Messenger of Allah [SAW] said: 'Defaming a Muslim is evildoing and fighting him is Kufr.'" I said to Abu Wa'il: "Did you hear it from 'Abdullah?" He said: "Yes."
Hadith ReferenceSunan an-Nasa'i / The Book Of Fighting (The Prohibition Of Bloodshed) / Hadith: 4115