The Messenger of Allah ﷺ said, "Insulting a Muslim is wickedness, and fighting him is disbelief."
حدثنا محمود بن غيلان حدثنا وكيع عن سفيان عن زبيد عن أبي وائل
قال رسول الله ﷺ سباب المسلم فسوق وقتاله كفر
Agreed upon [by Bukhari and Muslim]. Muslim narrated it in the Book of Faith, chapter on the statement of the Prophet ﷺ, "Reviling a Muslim is wickedness and fighting him is disbelief," hadith no. 64, from the hadith of Sufyan Thawri. Bukhari narrated it, hadith no. 48, from the hadith of Zubayd, with the same wording.Hadith, "Whoever kills intentionally..." etc, previously mentioned at no. 1387, and it is a hasan hadith.