Musannaf Ibn Abi Shayba 37:571

Abu Usama narrated to us, from Awf, from Muhammad, who said: Ali delivered a sermon in Basra and said, "By Allah, I did not kill him, nor did I assist in his killing." When he descended, some of his companions said to him, "What have you done now? Your companions will disperse from you." When he returned to the pulpit, he said, "Whoever is asking about the blood of Uthman, then Allah killed him, and I am with Him." Muhammad said: This is a Quraishi statement that has two meanings.