Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "The flourishing of Bayt al-Maqdis is (the forerunner of) the ruin of Yathrib; the ruin of Yathrib is (the forerunner of) the outbreak of the great battle; the outbreak of the great battle is (the forerunner of) the conquest of Constantinople; and the conquest of Constantinople is (the forerunner of) the emergence of the Dajjal."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17350