Musannaf Ibn Abi Shayba 38:79

Abu Usama narrated to us, from Shu'bah, from Ibn 'Awn, from Abu al-Duha, who said: Sulayman ibn Surad al-Khuza'i said to al-Hasan ibn 'Ali: "Excuse me before the Commander of the Faithful, for what prevented me from the Day of the Camel was such and such." He said: So al-Hasan said: "I indeed saw him when the fighting intensified, seeking refuge with me and saying: 'O Hasan, I wish I had died twenty years before this.'"