Musnad Ahmad 5:203

Abu al-Nadr narrated to us, al-Ashja‘i narrated to us, from Sufyan, from Jabir, from ‘Abdullah ibn Naji, from ‘Ali, from the Prophet, may Allah bless him and grant him peace, who said: We mentioned the Dajjal in the presence of the Prophet, may Allah bless him and grant him peace, while he was sleeping. He woke up with his complexion reddened, and he said: "Other than that is more fearful to me for you," and he mentioned a word.