Musannaf Ibn Abi Shayba 38:92

Yahya ibn Adam narrated to us, he said: Abu Bakr ibn Ayyash narrated to us, he said: Suhayb al-Faq'asi Abu Asad narrated to us, from his uncle, who said: "The pegs of our tents on the day of Siffin were nothing but the slain, and we were not able to eat food because of the stench." He said: And a man said, "Who will call for the mule for the day of the disbelief of the people of Sham?" He said: So he said, "From disbelief they fled."