"It is not permissible to kill a Muslim except in one of three cases: A adulterer who has been married, who is to be stoned; a man who kills a Muslim deliberately; and a man who leaves Islam and wages war against Allah, the Mighty and Sublime, and His Messenger, who is to be killed, crucified or banished from the land."  

عَنْ رَسُولِ اللَّهِ ﷺ أَنَّهُ قَالَ لاَ يَحِلُّ قَتْلُ مُسْلِمٍ إِلاَّ فِي إِحْدَى ثَلاَثِ خِصَالٍ زَانٍ مُحْصَنٍ فَيُرْجَمُ وَرَجُلٌ يَقْتُلُ مُسْلِمًا مُتَعَمِّدًا وَرَجُلٌ يَخْرُجُ مِنَ الإِسْلاَمِ فَيُحَارِبُ اللَّهَ ﷻ وَرَسُولَهُ فَيُقْتَلُ أَوْ يُصَلَّبُ أَوْ يُنْفَى مِنَ الأَرْضِ  

"I heard Abu Juhaifah say: 'We asked 'Ali: "Do you have anything from the Messenger of Allah apart from the Qur'an?" He said: "No, by the One who splits the seeds and creates the soul, unless Allah gives a slave understanding of His Book, or except this sheet." I said: "What is in the sheet?" He said: "In it are (the regulations concerning) blood money and the freeing of captives and (the rule) that no Muslim should be killed for killing a disbeliever."  

سَمِعْتُ أَبَا جُحَيْفَةَ يَقُولُ سَأَلْنَا عَلِيًّا فَقُلْنَا هَلْ عِنْدَكُمْ مِنْ رَسُولِ اللَّهِ ﷺ شَىْءٌ سِوَى الْقُرْآنِ فَقَالَ لاَ وَالَّذِي فَلَقَ الْحَبَّةَ وَبَرَأَ النَّسَمَةَ إِلاَّ أَنْ يُعْطِيَ اللَّهُ ﷻ عَبْدًا فَهْمًا فِي كِتَابِهِ أَوْ مَا فِي هَذِهِ الصَّحِيفَةِ قُلْتُ وَمَا فِي الصَّحِيفَةِ قَالَ فِيهَا الْعَقْلُ وَفِكَاكُ الأَسِيرِ وَأَنْ لاَ يُقْتَلَ مُسْلِمٌ بِكَافِرٍ  

"Ali said: 'The Messenger of Allah did not tell me anything that he did not tell the people, except what is in a sheet in the sheath of my word.' They did not leave him alone until he brought out the sheet, and in it (were the words): 'The lives of the believers are equal in value, and they hasten to support the asylum granted by the least of them, and they are one against others. But no believer may be killed in return for a disbeliever, nor one with a covenant while his covenant is in effect."  

عَلِيٌّ مَا عَهِدَ إِلَىَّ رَسُولُ اللَّهِ ﷺ بِشَىْءٍ دُونَ النَّاسِ إِلاَّ فِي صَحِيفَةٍ فِي قِرَابِ سَيْفِي فَلَمْ يَزَالُوا بِهِ حَتَّى أَخْرَجَ الصَّحِيفَةَ فَإِذَا فِيهَا الْمُؤْمِنُونَ تَكَافَأُ دِمَاؤُهُمْ يَسْعَى بِذِمَّتِهِمْ أَدْنَاهُمْ وَهُمْ يَدٌ عَلَى مَنْ سِوَاهُمْ لاَ يُقْتَلُ مُؤْمِنٌ بِكَافِرٍ وَلاَ ذُو عَهْدٍ فِي عَهْدِهِ  

"What the people have been hearing from you has become widespread. If the Messenger of Allah told you anything, then tell us," He said: "The Messenger of Allah did not tell me anything that he did not tell the people, except that in the sheath of my sword there is a sheet, in which it says: 'The lives of the believers are equal in value, 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."' It is an abridgement of it.  

أَنَّهُ قَالَ لِعَلِيٍّ إِنَّ النَّاسَ قَدْ تَفَشَّغَ بِهِمْ مَا يَسْمَعُونَ فَإِنْ كَانَ رَسُولُ اللَّهِ ﷺ عَهِدَ إِلَيْكَ عَهْدًا فَحَدِّثْنَا بِهِ قَالَ مَا عَهِدَ إِلَىَّ رَسُولُ اللَّهِ ﷺ عَهْدًا لَمْ يَعْهَدْهُ إِلَى النَّاسِ غَيْرَ أَنَّ فِي قِرَابِ سَيْفِي صَحِيفَةً فَإِذَا فِيهَا الْمُؤْمِنُونَ تَتَكَافَأُ دِمَاؤُهُمْ يَسْعَى بِذِمَّتِهِمْ أَدْنَاهُمْ لاَ يُقْتَلُ مُؤْمِنٌ بِكَافِرٍ وَلاَ ذُو عَهْدٍ فِي عَهْدِهِ مُخْتَصَرٌ