Musnad Abu Ya'la al-Mawsili 104:1

Hadba narrated to us, Hammam narrated to us, from Qatada, from Muhammad ibn Sirin, that a man in Kufa testified that Uthman, may Allah be pleased with him, was killed as a martyr. The guards (Zabaniya) seized him and brought him up to Ali, may Allah be pleased with him, and said, "Were it not that you forbid us, or that you had forbidden us from killing anyone, we would have killed him. This man claims that he testifies that Uthman, may Allah be pleased with him, was killed as a martyr." The man said to Ali, may Allah be pleased with him, "And you, do you testify? Do you remember that I came to the Messenger of Allah, may Allah bless him and grant him peace, and asked him, and he gave me? And I came to Abu Bakr, may Allah be pleased with him, and asked him, and he gave me? And I came to Umar, may Allah be pleased with him, and asked him, and he gave me? And I came to Uthman, may Allah be pleased with him, and asked him, and he gave me?" He said, "So I came to the Messenger of Allah, may Allah bless him and grant him peace, and said, 'O Messenger of Allah, supplicate to Allah to bless me.' The Prophet, may Allah bless him and grant him peace, said, 'How could it not be blessed for you, when a Prophet, a Truthful One (Siddiq), and two martyrs have given to you? And a Prophet, a Truthful One, and two martyrs have given to you? And a Prophet, a Truthful One, and two martyrs have given to you?'"