It was narrated from ‘Ali (رضي الله عنه) that The Messenger of Allah (ﷺ) said: `The believers are equal in respect of blood and they are one against their enemies; protection given even by the least among them is to be honoured, but no believer is to be killed (in retaliation) for a disbeliever and no one who has a covenant is to be killed during the covenant.`
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَبْد اللَّهِ، حَدَّثَنِي عُبَيْدُ اللَّهِ بْنُ عُمَرَ الْقَوَارِيرِيُّ، حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ الْوَاحِدِ بْنِ أَبِي حَزْمٍ، حَدَّثَنَا عُمَرُ بْنُ عَامِرٍ، عَنْ قَتَادَةَ، عَنْ أَبِي حَسَّانَ، عَنْ عَلِيٍّ، رَضِيَ اللَّهُ عَنْهُ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ الْمُؤْمِنُونَ تَكَافَأُ دِمَاؤُهُمْ وَهُمْ يَدٌ عَلَى مَنْ سِوَاهُمْ يَسْعَى بِذِمَّتِهِمْ أَدْنَاهُمْ أَلَا لَا يُقْتَلُ مُؤْمِنٌ بِكَافِرٍ وَلَا ذُو عَهْدٍ فِي عَهْدِهِ.
sunnah.com