Sunan an-Nasa'i 4113
سنن النسائي#4113Sahihأَخْبَرَنَا 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
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahSahih Muquf
Al-AlbaniSahih Muquf
Zubair Ali ZaiHasan
In-book reference: 37:148