Musnad Abu Ya'la al-Mawsili 160:153

Muhammad ibn Bakkar narrated to us, Abu Ma'shar narrated to us, from Sa'id, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) rode to the gathering place of the torrents (Majma' al-Suyul) and said: "Shall I not inform you of the location of the Dajjal in relation to Medina?" He said: "This is his location," meaning Medina. "He shall not be able to enter it. At every mountain pass of its mountain passes, there is an angel with his weapon drawn. The Dajjal shall not enter it."