Musnad Ahmad 595:15

'Ali ibn 'Ayyash narrated to us, Layth ibn Sa'd narrated to us, Musa ibn 'Ali narrated to us, from his father, from al-Mustawrid al-Fihri, that he said to 'Amr ibn al-'As: "The Hour will be established while the Romans are the most numerous of people." 'Amr ibn al-'As said to him: "Look at what you are saying." He said: "I am telling you what I heard from the Messenger of Allah, peace and blessings of Allah be upon him." 'Amr ibn al-'As said: "If you have said that, then they indeed possess four qualities: they are the quickest of people to return to the attack after a retreat, they are the best of people toward the destitute, the poor, and the weak, they are the most forbearing of people during a tribulation, and the fourth is a good and beautiful one: they are the most resistant of people to the oppression of kings."