It is narrated from Sayyiduna Amr bin Awf bin Milhah al-Muzani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "You will soon fight the Banu al-Asfar (the Romans) and kill them, and the believers who come after you will also fight them. The believers who strive in the path of Allah will go out against them, not caring for the blame of any blamer in the matter of Allah, until Allah conquers Constantinople and Rumiyyah for them through tasbih and takbir. Its fortress will be brought down, and they will obtain great wealth in it, so much so that they will divide the wealth (measuring it) with shields. And a caller will cry out: O people of Islam, the Masih al-Dajjal has emerged in your lands and among your offspring! They will say: Who is this caller? And they will not know who he is. So they will say: Look, and form a sound opinion: send a vanguard to Lud; if the Masih has emerged, it will come to you with news of him. So they will send the vanguard to Lud, then they will say: Let us march towards them; if it is he (al-Dajjal), we will fight him until Allah judges between us, and He is the best of judges; and if it is otherwise, then these are your own lands and your own clans, and you will return to them."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14101