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
Sayyiduna Abdullah (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) said: "The blood of a Muslim is not lawful except for one of three reasons: he is killed in retaliation (qisas), or a married adulterer, or an apostate who abandons the religion and the community."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16818
Ikrimah (may Allah have mercy on him) said that when Ibn Abbas (may Allah be pleased with him) learned that Ali (may Allah be pleased with him) had burned the apostates and the heretics (zanadiqah), he said: Had it been me, I would not have burned them; rather I would have killed them, because the Prophet (peace and blessings be upon him) said: "Whoever changes his religion and apostatises, kill him." And I would not have burned them because the Prophet (peace and blessings be upon him) said: "It is not fitting for anyone to punish (anyone) with the punishment of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16820
Sayyiduna Abu Musa (may Allah be pleased with him) said: I came to the Prophet (peace and blessings be upon him), and with me were two men of the Ash'aris, one on my right and the other on my left. The Prophet (peace and blessings be upon him) was using the tooth-stick (miswak). Both of them asked the Prophet (peace and blessings be upon him) to appoint them as officials. He (peace and blessings be upon him) remained silent, then said: "O Abu Musa! What do you say?" I said: By the One who sent you with the truth, I did not know why these two had come or what they intended. He said: I could see the tooth-stick under his (peace and blessings be upon him) lip, drawn back. He (peace and blessings be upon him) said: "We do not appoint as an official one who asks for it himself; but you, O Abu Musa, go to Yemen." Then he (peace and blessings be upon him) sent Sayyiduna Mu'adh (may Allah be pleased with him) after him. When Sayyiduna Mu'adh (may Allah be pleased with him) arrived, he said: Come down, and placed a cushion for him. Then he saw a man who was tied up. He asked: What is this? He replied: This man was a Jew, he became Muslim, but then he became a Jew again. Sayyiduna Mu'adh (may Allah be pleased with him) said: I will not sit down until he is killed, for this is the judgement of Allah and His Messenger (peace and blessings be upon him) in this matter (he said this three times). So he was killed. Then the two of them (may Allah be pleased with them both) sat and discussed the night prayer (qiyam al-layl), and Sayyiduna Mu'adh (may Allah be pleased with him) said: I both stand (in prayer) and sleep, and in my sleep I hope from Allah for the same (reward) I hope for in my standing.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16822