Musannaf Ibn Abi Shayba 27:827

Isa ibn Yunus narrated to us, from Abu Bakr, from Abu al-Zahiriyah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The stronghold of the Muslims during the great battles (al-malahim) is Damascus. Their stronghold against the Dajjal is Bayt al-Maqdis (Jerusalem). And their stronghold against Gog and Magog is Mount Tur."