Musannaf Ibn Abi Shayba 38:56

Affan narrated to us, he said: Abu 'Awanah narrated to us, from Ibrahim ibn Muhammad ibn al-Muntasir, from his father, from 'Ubayd ibn Nadlah, from Sulayman ibn Surad, who said: I came to 'Ali on the Day of the Camel, and with him were al-Hasan and some of his companions. When 'Ali saw me, he said: "O son of Surad, you hesitated, you wavered, and you waited. How do you see what God has done? God has made [me] independent of you." I said: "O Commander of the Faithful, the whip is being smeared with clay, and there remain matters in which you will recognize your enemy from your friend." He said: When al-Hasan stood up, I met him and said: "I do not see that you have helped me at all, nor have you excused me before the man, even though I was eager for you to bear witness with him." He said: "He blames you for what he blames you for. He said to me on the Day of the Camel, when the people marched toward one another: 'O Hasan, may your mother be bereaved of you—or may your mother be childless—what is your opinion of my affair? He has brought these two armies together, and by God, I do not see any good after this.'" He said: I said: "Be silent, lest your companions hear you and say you have doubted, and then they kill you."