عن عبد الله بن مسعود رضي الله عنه عن النبي صلى الله عليه وسلم قال: «سِبابُ المسلم فسوق، وقتاله كفر».
[صحيح] - [متفق عليه]
المزيــد ...
‘Abdullah ibn Mas‘ūd (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said:
"Reviling a Muslim is Fusūq (deobedience) and fighting him is Kufr (disbelief)."
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 48]
The Prophet (may Allah's peace and blessings be upon him) forbade the Muslim from cursing and reviling his Muslim brother, stating that this is an act of Fusūq, which means disobeying Allah and His Messenger (may Allah's peace and blessings be upon him), and fighting his Muslim brother is an act of Kufr, yet it is minor Kufr.