Sunan Ibn Majah 69
سنن ابن ماجه#69SahihIt was narrated that 'Abdullah said:"The Messenger of Allah (ﷺ) said: 'Verbally abusing a Muslim is immorality and fighting him is Kufr (disbelief)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Bukhari