Musnad Ahmad 830:102

Muhammad ibn Bishr narrated to us, Mis'ar narrated to us, Sa'd ibn Ibrahim narrated to us, from his father, from Abu Bakrah, from the Prophet, peace and blessings of Allah be upon him, who said: "The terror of the False Messiah (Al-Masih ad-Dajjal) shall not enter Medina. It will have, on that day, seven gates; at every gate there will be two angels."