Bulugh al-Maram, Book 9, Hadith 1205 (English) ⓘ

The previous tradition was also transmitted by Ahmad, An-Nasa’i and Abu Dawud on the authority of 'Ali with a different chain of narrators where he said, ‘The blood of one Muslim (his life) is equivalent to the blood of another Muslim (i.e. equal in Qisas and blood money), the protection of Allah is one (and is equally) extended to the most humble of the believers (i.e. if a Muslim gives protection to a man or to a group of men, they should all help him even is he was the most humble of them). Believers are all like one hand against their enemies. No believer is to be killed for a disbeliever (i.e. in Qisas), nor should one who has a covenant with the Muslims be killed while his covenant holds.’ Al-Hakim graded it as Sahih.

وَأَخْرَجَهُ أَحْمَدُ, وَأَبُو دَاوُدَ, وَالنَّسَائِيُّ: مِنْ وَجْهٍ آخَرَ عَنْ عَلِيٍّ وَقَالَ فِيهِ: { اَلْمُؤْمِنُونَ تَتَكَافَأُ دِمَاؤُهُمْ, وَيَسْعَى بِذِمَّتِهِمْ أَدْنَاهُمْ, وَهُمْ يَدٌ عَلَى مَنْ سِوَاهُمْ, وَلَا يُقْتَلُ مُؤْمِنٌ بِكَافِرٍ, وَلَا ذُو عَهْدٍ فِي عَهْدِهِ }.‏ وَصَحَّحَهُ اَلْحَاكِمُ 1‏.‏ ‏1 ‏- صحيح.‏ رواه أحمد (122)‏، وأبو داود (4530)‏، والنسائي (89 ‏- 20)‏ وزادوا جميعا: "ومن أحدث حدثا أو آوى محدثا، فعليه لعنة الله والملائكة والناس أجمعين".‏