لَا يَحِلُّ دَمُ امْرِئٍ مُسْلِمٍ يَشْهَدُ أَنْ لَا إِلَٰهَ إِلَّا اللَّهُ وَأَنِّي رَسُولُ اللَّهِ إِلَّا بِإِحْدَى ثَلَاثٍ
The life of a Muslim who testifies to Allah’s oneness and Muhammad’s ﷺ messengership is inviolable, except in three specified legal cases. (Sahih al-Bukhari; Sahih Muslim)
The starting principle is sanctity of life. The specified exceptions concern lawful adjudication, not an individual’s independent authority to punish. The narration cannot justify unauthorized violence or private enforcement.