The Prophet (SAWA) said, ‘If a man trusts you with his blood [i.e. that you will spare his life] then do not kill him.
رسولُ اللهِ (صَلَّيَ اللهُ عَلَيهِ وَ آلِهِ) : إذا أمِنَكَ الرّجُلُ على دمِهِ فلا تَقْتُلْهُ.
Similar narrations
Mīzān al-Ḥikma #286The Prophet (SAWA) said, ‘When a man assures another of sparing his life and then kills him, [know that] I renounce the killer, even if the...