Sayyiduna Abu Umamah bin Sahl bin Hunayf (may Allah be pleased with him) said: We were with Sayyiduna Uthman (may Allah be pleased with him) when he was confined in his house, and we entered a place from where we could hear the voices of the people. Sayyiduna Uthman (may Allah be pleased with him) went in and then came out, and his colour had changed. We asked: O Commander of the Believers! What is the matter? He said: The people are thinking of killing me; until today I had not been certain of this. We said: O Commander of the Believers! Allah will help you. Then he said: Why do these people want to kill me, when I have heard the Messenger of Allah (peace and blessings be upon him) say: "A Muslim may be killed only for one of three reasons: 1. he becomes an apostate, 2. he commits adultery after marriage, 3. he is killed in retaliation (qisas)." By Allah! I have never committed adultery, neither before Islam nor after Islam; after Islam I cannot even imagine leaving it; and I have not killed anyone. So why do these people want to kill me?
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15843