حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، قَالَ: حَدَّثَنَا شُعْبَةُ، عَنْ زُبَيْدٍ قَالَ: سَمِعْتُ أَبَا وَائِلٍ، عَنْ عَبْدِ اللهِ، عَنِ النَّبِيِّ صلى الله عليه وسلم: سِبَابُ الْمُسْلِمِ فُسُوقٌ، وَقِتَالُهُ كُفْرٌ.
'Abdullah reported that the Prophet, may Allah bless him and grant him peace, said, "Reviling a Muslim is deviant behaviour and killing him is disbelief."
Reported by Al-Bukhari (No. 48, 6044, 7076), Muslim (No. 64a), At-Tirmidhi (No. 1983, 2635), An-Nasa’i (No. 4105, 4107, 4108, 4109, 4110, 4111, 4112), Ibn Majah (No. 69, 3939) and Ahmad (No. 3465, 3708, 3916, 4115). Cited in Al-Adab al-Mufrad (No. 431).