Musannaf Ibn Abi Shayba 24:171

Narrated to us Abd al-A’la, from al-Jurayri, from al-‘Ala’, who said: They said to Mutarrif, "This is Abd al-Rahman ibn al-Ash’ath who has arrived." Mutarrif said, "By Allah, two matters have caused me doubt: If he prevails, the religion of Allah will not be upheld; and if he is defeated, they will remain humiliated until the Day of Resurrection."