We were with Uthman while he was besieged in his house. The house had an entryway where anyone who stepped inside could hear what was being said out on the paved area. Uthman entered it and came back out to us with his color changed.He said, "They are threatening to kill me right now."We said, "Allah will suffice you against them, Commander of the Faithful."He said, "Why would they kill me? I heard the Messenger of Allah ﷺ say, 'The blood of a Muslim is not lawful to shed except for one of three reasons, disbelief after Islam, adultery after marriage, or taking a life without right.' By Allah, I never committed adultery, neither in the time of ignorance nor in Islam. I never wished to exchange my religion for any other since Allah guided me, and I never killed anyone. So for what would they kill me?"
حدثنا سليمان بن حرب حدثنا حماد بن زيد عن يحيى ابن سعيد
كنا مع عثمان وهو محصور في الدار وكان في الدار مدخل من دخله سمع كلام من على البلاط فدخله عثمان فخرج إلينا وهو متغير لونه فقال إنهم ليتواعدونني بالقتل آنفا قال قلنا يكفيكهم الله يا أمير المؤمنين قال ولم يقتلونني سمعت رسول الله ﷺ يقول لا يحل دم امرئ مسلم إلا بإحدى ثلاث كفر بعد إسلام أو زنا بعد إحصان أو قتل نفس بغير نفس فوالله ما زنيت في جاهلية ولا في إسلام قط ولا أحببت أن لي بديني بدلا منذ هداني الله ولا قتلت نفسا فبم يقتلونني
Its isnad is sahih. Tirmidhi narrated it in Kitab al-Fitan, chapter "It is not lawful to shed the blood of a Muslim except for one of three reasons," hadith 2158, and Nasai, hadith 4024, and Ibn Majah, hadith 2533, from the hadith of Hammad bin Zayd through this route, and Ibn Jarud graded it sahih, hadith 836.