(Imam Bukhari narrates that) Muhammad bin Ar'arah narrated to us, he said: Shu'bah narrated to us, from Zubaid, he said: I asked Abu Wa'il about the Murji'ah, he said: Hazrat Abdullah (may Allāh be pleased with him) narrated to me that the Prophet ﷺ said:
Abusing a Muslim is transgression (fisq), and fighting him is disbelief (kufr).
حَدَّثَنَا مُحَمَّدُ بْنُ عَرْعَرَةَ قَالَ: حَدَّثَنَا شُعْبَةُ، عَنْ زُبَيْدٍ قَالَ
سَأَلْتُ أَبَا وَائِلٍ عَنِ الْمُرْجِئَةِ فَقَالَ: حَدَّثَنِي عَبْدُ اللهِ: أَنَّ النَّبِيَّ ﷺ قَالَ: سِبَابُ الْمُسْلِمِ فُسُوقٌ وَقِتَالُهُ كُفْرٌ.
Reference: Sahih Al Bukhari 48