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]‏ .‏