Musannaf Ibn Abi Shayba 38:54

Ya'la ibn 'Ubayd narrated to us, he said: Isma'il ibn Abi Khalid narrated to us, from Abu al-Duha, from Abu Hafs, who said: 'Ali heard a voice on the day of the Camel [battle] from the direction of the Mother of the Believers. He said: "Look at what they are saying." They returned and said: "They are calling out for the killers of 'Uthman." He said: "O Allah, bring down upon the killers of 'Uthman disgrace."