(4) باب سِبَابُ الْمُسْلِمِ فُسُوقٌ وَقِتَالُهُ كُفْرٌ
It was narrated from Sa'd that the Messenger of Allah (ﷺ) said:
"Verbally abusing a Muslim is Fusuq (disobedience) and fightinghimis Kufr." (IT)
Reference (IT): Sunan Ibn Majah 3941 (IT)
In-book reference (IT): Book 36, Hadith 16 (IT)
English translation (IT): Vol. 5, Book 36, Hadith 3941 (IT)