مُسْنَدُ أَحْمَدَ
Musnad Ahmad 1537
Musnad Abu Ishaq Sa'd bin Abi Waqqas
It was narrated from Muhammad bin Sa"d bin Malik, from his father, that the Prophet (ﷺ) said: “Fighting a Muslim is kufr (disbelief) and reviling him is fisq (evildoing)."
Musnad Ahmad 1537Sahih (Darussalam) []