Narrator:Abdullah ibn Mas‘ūd
حَدَّثَنَا عُمَرُ بْنُ حَفْصٍ، حَدَّثَنِي أَبِي، حَدَّثَنَا الأَعْمَشُ، حَدَّثَنَا شَقِيقٌ، قَالَ قَالَ عَبْدُ اللَّهِ قَالَ النَّبِيُّ صلى الله عليه وسلم "
سِبَابُ الْمُسْلِمِ فُسُوقٌ، وَقِتَالُهُ كُفْرٌ "
Narrated `Abdullah:
The Prophet, said, "Abusing a Muslim is Fusuq (evil doing) and killing him is Kufr (disbelief).
Reported by Al-Bukhari (No. 7076, 48, 6044), 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).