Jami` at-Tirmidhi 2635
جامع الترمذي#2635SahihNarrated Ibn Mas'ud:that the Messenger of Allah (ﷺ) said: "Verbally abusing a Muslim is disobedience and fighting him is disbelief
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 40:30