Mishkat al-Masabih 3466
Abu Umama b. Sahl b. Hunaif told that when ‘Uthman b. ‘Affan was besieged he looked down and said:
I adjure you by God. Are you aware that God’s Messenger said, “It is not lawful to kill a man who is a Muslim except for one of three reasons: fornication after marriage, or unbelief after accepting Islam, or wrongfully killing someone, for which he may be killed”? I swear by God that I have not committed fornication before or after the coming of Islam, or apostatised since I swore allegiance to God's Messenger, or killed anyone whom God has declared inviolate; so for what reason do you want to kill me? 

Tirmidhi, Nasa'i and Ibn Majah transmitted it, and Darimi gives the wording of the tradition.
وَعَنْ أَبِي أُمَامَةَ بْنِ سَهْلِ بْنِ حُنَيْفٍ أَنَّ عُثْمَانَ بْنَ عَفَّانَ رَضِيَ اللَّهُ عَنْهُ أَشْرَفَ يَوْمَ الدَّارِ فَقَالَ: أَنْشُدُكُمْ بِاللَّهِ أَتَعْلَمُونَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: 
" لَا يَحِلُّ دَمُ امْرِئٍ مُسْلِمٍ إِلَّا بِإِحْدَى ثلاثٍ: زِنىً بَعْدَ إِحْصَانٍ أَوْ كُفْرٌ بَعْدَ إِسْلَامٍ أَوْ قتْلِ نفْسٍ بِغَيْر حق فَقتل بِهِ "؟ فو الله مَا زَنَيْتُ فِي جَاهِلِيَّةٍ وَلَا إِسْلَامٍ وَلَا ارْتَدَدْتُ مُنْذُ بَايَعْتُ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَلَا قَتَلْتُ النَّفْسَ الَّتِي حَرَّمَ اللَّهُ فَبِمَ تَقْتُلُونَنِي؟ رَوَاهُ التِّرْمِذِيُّ وَالنَّسَائِيُّ وَابْنُ مَاجَه وللدارمي لفظ الحَدِيث