Sunan an-Nasa'i · Hadith 4112
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ أَبِي وَائِلٍ، قَالَ قَالَ عَبْدُ اللَّهِ سِبَابُ الْمُسْلِمِ فُسُوقٌ وَقِتَالُهُ كُفْرٌ .
It was narrated that Abu Wa'il said:"'Abdullah said: 'Defaming a Muslim is evildoing and fighting him is Kufr
Sahih Muquf · Abu GhuddahSahih Muquf · Al-AlbaniSahih · Zubair Ali Zai