Musannaf Ibn Abi Shayba 37:606

Al-Fadl ibn Dukayn narrated to us, he said: Sa'id ibn 'Abd al-Rahman narrated to us, he said: Muhammad ibn Sirin narrated to us, he said: When 'Uthman was killed, 'Adi ibn Hatim said: "Two goats will not butt heads over it." Then, when the day of Siffin came, his eye was gouged out. It was said to him: "Did two goats not butt heads over the killing of 'Uthman?" He said: "Yes, and many eyes will be gouged out because of it."