4049An NasaiSahih (Darussalam)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.'"Reference: Sunan an-Nasa'i 4112 In-book : Book 37, Hadith 147 English translation : Vol. 5, Book 37, Hadith 4117