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»
Ali reported the Prophet (sallallahu alayhi wa sallam) as saying, “The lives of all Muslims are equal; the lowliest of them can guarantee their protection, the most distant can keep others from breaking protection he has given,* and they are one band against others. A Muslim must not be killed for an infidel, nor must one who has been given a covenant be killed while his covenant holds.” Abu Dawud and Nasai transmitted it, and Ibn Majah transmitted it on the authority of Ibn Abbas * The interpretation which seems to be preferred is that no matter how far one may live from the land of infidels, any protection one may guarantee to an infidel must be respected by all Muslims.
Another possible explanation is that when a detachment is sent ahead into infidel country those who remain behind them are entitled to their portion of any spoil they take, but it is felt that this meaning does not suit the context. The Arabic words are wa-yaruddu ‘alaihim aqsahum.’