The Messenger of Allah ﷺ said, "The Great Battle, the conquest of Constantinople, and the emergence of the Dajjal will all occur within seven months."
حدثنا أبو المغيرة وأبو اليمان قالا ثنا أبو بكر حدثني الوليد بن سفيان بن أبي مريم عن يزيد بن قطيب السكوني عن أبي بحرية قال أبو المغيرة في حديثه عن عبد الله بن قيس قال سمعت
قال رسول الله ﷺ الملحمة العظمى وفتح القسطنطينية وخروج الدجال في سبعة أشهر
Its isnad is daif because of Abu Bakr bin Abu Maryam Ghassani, and they also considered Walid bin Sufyan bin Abu Maryam unknown, though Ibn Hibban rated him trustworthy. In al-Kashif it says he was rated trustworthy, but he was deemed unknown in al-Mizan and al-Mughni. In al-Taqrib it says he is unknown. This hadith was already given more completely at 21922 with a sahih chain, and it should be taken from there, not from here. I also think one of the narrators undoubtedly made a mistake in it. For if what is meant by the conquest of Constantinople is the conquest that actually took place, and the city is the very same city, then this is not acceptable and does not hold together. But if the Prophet ﷺ, assuming the hadith is sahih, meant by Constantinople Rome and what lies beyond it, then we believe in what has come down from the Messenger of Allah ﷺ.