4050An NasaiSahih (Darussalam)أَخْبَرَنَا مُحَمَّدُ بْنُ الْعَلاَءِ، عَنْ أَبِي مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ شَقِيقٍ، عَنْ عَبْدِ اللَّهِ، قَالَ قِتَالُ الْمُؤْمِنِ كُفْرٌ وَسِبَابُهُ فُسُوقٌ .It was narrated that 'Abdullah said:"Fighting a believer is Kufr and defaming him is evildoing."Reference: Sunan an-Nasa'i 4113 In-book : Book 37, Hadith 148 English translation : Vol. 5, Book 37, Hadith 4118