Uthman bin Affan looked down upon them and heard them talking about killing him. He said, "They are threatening me with death, but why would they kill me? I heard the Messenger of Allah ﷺ say, 'The blood of a Muslim is not lawful except in one of three cases. A man who commits adultery while married, so he is stoned. A man who kills another person without just cause. Or a man who apostatizes after embracing Islam.' By Allah, I never committed adultery, neither in the days of ignorance nor in Islam, nor have I killed a Muslim, nor have I apostatized since I embraced Islam."
حدثنا أحمد بن عبدة أنبأنا حماد بن زيد عن يحيى بن سعيد
أن عثمان بن عفان أشرف عليهم فسمعهم وهم يذكرون القتل فقال إنهم ليتواعدوني بالقتل فلم يقتلوني وقد سمعت رسول الله ﷺ يقول لا يحل دم امرئ مسلم إلا في إحدى ثلاث رجل زنى وهو محصن فرجم أو رجل قتل نفسا بغير نفس أو رجل ارتد بعد إسلامه فوالله ما زنيت في جاهلية ولا في إسلام ولا قتلت نفسا مسلمة ولا ارتددت منذ أسلمت
Its isnad is sahih. Abu Dawud narrated it in the Book of Diyat, chapter on the imam ordering pardon in a case of bloodshed, hadith 4502, from the hadith of Hammad, with this wording. Tirmidhi graded it hasan, hadith 2158, and Ibn Jarud graded it sahih, hadith 836.