Musnad Ahmad 31:328

'Abd al-Razzaq narrated to us, Ma'mar informed us, from al-Zuhri, who said: 'Ubayd Allah ibn 'Abd Allah informed me that Abu Sa'id al-Khudri said: The Messenger of Allah (peace and blessings of Allah be upon him) narrated to us a long hadith about the Dajjal. He said, among what he narrated to us: "The Dajjal will come, and it is forbidden for him to enter the mountain passes of Medina. So a man will go out to him on that day, who is the best of people—or among the best of them—and he will say: 'I bear witness that you are the Dajjal whom the Messenger of Allah (peace and blessings of Allah be upon him) told us about.' The Dajjal will say: 'Do you see, if I kill this one and then bring him back to life, will you doubt the matter?' They will say: 'No.' So he will kill him, then bring him back to life. When he is brought back to life, he will say: 'By Allah, I have never been more insightful regarding you than I am right now.' He said: So he will want to kill him a second time, but he will not be given power over him."