Musnad Ahmad 6:22

Yazid ibn Abd Rabbih narrated to us, Al-Harith ibn Ubaydah narrated to us, Muhammad ibn Abd al-Rahman ibn Mujbar narrated to me, from his father, from his grandfather, that Uthman, may Allah be pleased with him, looked down upon those who had besieged him and greeted them, but they did not return his greeting. Uthman said, "Is Talhah among the people?" Talhah said, "Yes." He said, "To Allah we belong and to Him we shall return. I greet a people among whom you are, and they do not return it." He said, "I have returned it." He said, "The response is not like this; I hear you and you do not hear me, O Talhah? I adjure you by Allah, did you hear the Prophet, may Allah bless him and grant him peace, say: 'The blood of a Muslim is not lawful except for one of three: that he disbelieves after his belief, or commits adultery after his chastity, or kills a soul, so he is killed for it'?" He said, "O Allah, yes." Uthman then said "Allahu Akbar" (God is the Greatest) and said, "By Allah, I have not denied Allah since I knew Him, nor have I committed adultery in the Age of Ignorance or in Islam—having abandoned it in the Age of Ignorance out of dislike, and in Islam out of chastity—and I have not killed a soul for which it would be lawful to kill me."