It was narrated from 'Ali, may Allah be please with him that the Prophet said:"The lives of the believers are equal in value, and they are one against others, and they hasten to support the asylum granted by the least of them. But no believer may be killed in return for a disbeliever, nor one with a covenant while his covenant is in effect."
أَخْبَرَنِي أَبُو بَكْرِ بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا الْقَوَارِيرِيُّ، قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ الْوَاحِدِ، قَالَ حَدَّثَنَا عُمَرُ بْنُ عَامِرٍ، عَنْ قَتَادَةَ، عَنْ أَبِي حَسَّانَ، عَنْ عَلِيٍّ، رضى الله عنه أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " الْمُؤْمِنُونَ تَكَافَأُ دِمَاؤُهُمْ وَهُمْ يَدٌ عَلَى مَنْ سِوَاهُمْ يَسْعَى بِذِمَّتِهِمْ أَدْنَاهُمْ لاَ يُقْتَلُ مُؤْمِنٌ بِكَافِرٍ وَلاَ ذُو عَهْدٍ فِي عَهْدِهِ " .
Nesai
The Book of Oaths (qasamah), Retaliation and Blood Money • Hadith 4735