(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." (DE)
Reference (DE): Sunan Ibn Majah 3941 (DE)
In-book reference (DE): Book 36, Hadith 16 (DE)
English translation (DE): Vol. 5, Book 36, Hadith 3941 (DE)