Musnad Abu Ya'la al-Mawsili 105:9

Bandar narrated to us, Muhammad—meaning Ghundar—narrated to us, Shu'bah narrated to us, from 'Amr ibn Murrah, who said: I heard 'Abdullah ibn Salamah saying: I saw 'Ammar ibn Yasir on the day of Siffin, an elderly, tall, dark-skinned man, holding a spear in his hand, and his hand was trembling. He said: "By the One in Whose hand is my soul, I have fought with this banner alongside the Messenger of Allah (peace and blessings of Allah be upon him) three times, and this is the fourth. By the One in Whose hand is my soul, if they were to strike us until they reached the peaks of Hajar with us, we would know that we are upon the truth and that they are upon misguidance."