Sunan Ibn Majah
3940
Hasan Sahih+2

It was narrated from Abu Hurairah that the Prophet (ﷺ) said:“Verbally abusing a Muslim is Fusuq (disobedience) and fighting him is Kufr (ungratefulness to Allah).”

Hasan SahihAl-Albani
Hasan SahihMuhammad Fouad Abd al-Baqi