It was narrated that 'Abdullah said:
"The Messenger of Allah (ﷺ) said: 'Verbally abusing a Muslim is immorality and fighting him is Kufr (disbelief).'" (AR)
English reference (AR): Vol. 1, Book 1, Hadith 69 (AR)
Arabic reference (AR): Book 1, Hadith 72 (AR)