Mishkat al-Masabih
Mishkat al-Masabih 3475, 3476
وَعَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «الْمُسْلِمُونَ تَتَكَافَأُ دِمَاؤُهُمْ وَيَسْعَى بِذِمَّتِهِمْ أَدْنَاهُمْ وَيَرُدُّ عَلَيْهِمْ أَقْصَاهُمْ وَهُمْ يَدٌ عَلَى مَنْ سِوَاهُمْ أَلَا لَا يُقْتَلُ مُسْلِمٌ بِكَافِرٍ وَلَا ذُو عَهْدٍ فِي عَهْدِه» . رَوَاهُ أَبُو دَاوُد وَالنَّسَائِيّ وَرَوَاهُ ابْن مَاجَه عَن ابْن عَبَّاس
Ali reported from the Prophet that he said: ‘The lives of Muslims are equal. The lowliest among them may grant protection on their behalf, and the most distant among them may uphold it for them. They are united against all others. A Muslim is not to be killed for a non-Muslim, nor a person under a covenant while that covenant remains in force.’ Abu Dawud and al-Nasa'i transmitted it. Ibn Majah transmitted it from Ibn Abbas.
Translation notes
The Arabic phrase about the most distant person upholding protection is ambiguous. The English witness supplies multiple interpretations in an editorial footnote, which is not included here.