Abu Umamah bin Sahl bin Hunayf and Abdullah bin Amir bin Rabi'ah (may Allah be pleased with them both) said: We were with Sayyiduna Uthman (may Allah be pleased with him) in the house while he was besieged. We entered the house at a place from which we could hear the talk of the people standing outside. One day Sayyiduna Uthman (may Allah be pleased with him) came out, and his colour had changed. We said: "O Commander of the Believers! Is everything well?" He said: "They want to kill me." We said: "Allah Almighty is sufficient for you against them." He said: "Why do they want to kill me, when I heard the Prophet (peace and blessings be upon him) say: 'The blood of a Muslim is lawful only for one of three reasons: an apostate who turns away from Islam, a married adulterer, and one who kills unjustly.' By Allah! I never committed adultery, neither in the Jahiliyyah nor in Islam, nor did I ever kill anyone unjustly since Allah Almighty guided me, and since I accepted Islam I have never even thought of turning away from it. So why do they want to kill me?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16817