The Prophet ﷺ said: The most merciful of the people in respect of killing are believers (in Allah).  

قَالَ رَسُولُ اللَّهِ ﷺ أَعَفُّ النَّاسِ قِتْلَةً أَهْلُ الإِيمَانِ  

Al-Hayyaj ibn Imran ibn Husayn reported that a slave of Imran ran away. He took a vow to Allah that if he overpowers him, he will cut off his head. He then sent me (to Samurah ibn Jundub) to ask him about this question for him. I came to Samurah ibn Jundub and asked him. He said: The Messenger of Allah ﷺ used to exhort us to give alms (sadaqah) and forbid us to mutilate (a slain). I then came to Imran ibn Husayn and asked him. He said: The Messenger of Allah ﷺ used to exhort us to give alms (sadaqah) and forbid us to mutilate (a slain).  

أَنَّ عِمْرَانَ أَبَقَ لَهُ غُلاَمٌ فَجَعَلَ لِلَّهِ عَلَيْهِ لَئِنْ قَدَرَ عَلَيْهِ لَيَقْطَعَنَّ يَدَهُ فَأَرْسَلَنِي لأَسْأَلَ لَهُ فَأَتَيْتُ سَمُرَةَ بْنَ جُنْدَبٍ فَسَأَلْتُهُ فَقَالَ كَانَ نَبِيُّ اللَّهِ ﷺ يَحُثُّنَا عَلَى الصَّدَقَةِ وَيَنْهَانَا عَنِ الْمُثْلَةِ فَأَتَيْتُ عِمْرَانَ بْنَ حُصَيْنٍ فَسَأَلْتُهُ فَقَالَ كَانَ رَسُولُ اللَّهِ ﷺ يَحُثُّنَا عَلَى الصَّدَقَةِ وَيَنْهَانَا عَنِ الْمُثْلَةِ