It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that he said: We came to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) came out to us cheerfully, with signs of joy evident on his blessed face. Whatever we asked him about, he informed us of it, and when we fell silent, he himself began speaking, until some young men of Banu Hashim passed by, among whom were Hasan and Husayn (may Allah be pleased with them both). When he (peace and blessings be upon him) saw them, his mood became troubled at their passing and his eyes overflowed with tears. We said: "O Messenger of Allah! We keep seeing something on your blessed face that grieves us." So he (peace and blessings be upon him) said: "Indeed, we are a household for whom Allah has chosen the Hereafter over this world. And indeed, after me my household will endure the hardships of exile and being driven from land to land, until black banners are raised from the direction of the east. They will ask for their right but it will not be given to them; then they will demand it but it will not be given to them; so they will fight and will be granted victory. So whoever among you or among your descendants lives to see that time, let him come to the Imam of my household, even if he has to crawl over snow, for they will be banners of guidance which they will hand over to a man of my household whose name will match my name and whose father's name will match my father's name. He will rule the earth and fill it with justice and equity just as it had been filled with oppression and tyranny."