It is narrated from Sayyiduna Mustawrid bin Shaddad (may Allah be pleased with him); he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "The Hour will be established while the Romans (Byzantines) are the most numerous of people." This reached Sayyiduna Amr bin al-As (may Allah be pleased with him), and he said: What are these hadiths that are being reported from you? Sayyiduna Mustawrid (may Allah be pleased with him) said to him: I said what I heard from the Messenger of Allah (peace and blessings be upon him). At that Sayyiduna Amr (may Allah be pleased with him) said: "If you have said that, then indeed they are the people who will be the most forbearing at the time of trial (fitnah), the most patient at the time of calamity, and the best in their treatment of their weak and their poor."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17867