Hadith 3939
Chapter 4: Verbally abusing a Muslim is Fusuq (disobedience) and fighting Him is Kufr (ungratefulness to Allah) - كتاب الفتن
حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا عِيسَى بْنُ يُونُسَ، حَدَّثَنَا الأَعْمَشُ، عَنْ شَقِيقٍ، عَنِ ابْنِ مَسْعُودٍ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " سِبَابُ الْمُسْلِمِ فُسُوقٌ وَقِتَالُهُ كُفْرٌ " .
It was narrated from Ibn Mas’ud that the Messenger of Allah (ﷺ) said:
“Verbally abusing a Muslim is Fusuq disobedience and fighting him is Kufr (ungratefulness to Allah).’”
Reference : Sunan Ibn Majah 3939
In-book reference : Book 36, Hadith 14