“Verbally abusing a Muslim is Fusuq (disobedience) and fighting him is Kufr.”

قَالَ رَسُولُ اللَّهِ ﷺ سِبَابُ الْمُسْلِمِ فُسُوقٌ وَقِتَالُهُ كُفْرٌ