insulting a Muslim is disobedience to Allah, and fighting with him is Kufr (disbelief). Agreed upon.
وَعَنْ اِبْنِ مَسْعُودٍ رضى الله عنه
قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -«سِبَابُ اَلْمُسْلِمِ فُسُوقٌ، وَقِتَالُهُ كُفْرٌ»
insulting a Muslim is disobedience to Allah, and fighting with him is Kufr (disbelief). Agreed upon.
صحيح. رواه البخاري (6044) ومسلم (64)
Who passed it on, from Ibn Hajar back to the one who was there.
The same words, in another collection.
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