Musannaf Ibn Abi Shayba 37:566

Muhammad ibn Bishr narrated to us, he said: Isma'il ibn Abi Khalid narrated to us, he said: Husayn, a man from Banu al-Harith, narrated to me, he said: A female captive of Zayd ibn Arqam informed me, she said: Ali came to visit Zayd ibn Arqam, and the people were with him. He said to the people: "Listen and be silent, for by Allah, you will not ask me today about anything except that I will inform you of it." Zayd said to him: "I adjure you by Allah, did you kill Uthman?" He lowered his head for a while, then said: "By the One who split the seed and created the soul, I did not kill him, nor did I order his killing, and it did not please me."