كتاب الجامع
16  
The Comprehensive Book
Bulugh al-Maram 1487
Ibn Mas'ud (RAA) narrated that the Messenger of Allah (ﷺ) said:
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 ‏- صلى الله عليه وسلم ‏-{ سِبَابُ اَلْمُسْلِمِ فُسُوقٌ, وَقِتَالُهُ كُفْرٌ } مُتَّفَقٌ عَلَيْهِ.‏ 1‏ .‏
Reference : Bulugh al-Maram 1487
In-book reference : Book 16, Hadith 1487
English translation : Book 16, Hadith 1530
Hadith Text
Reference