The emergence of the Mahdi (peace be upon him)

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."

It is narrated from Sayyiduna Hudhayfah (may Allah be pleased with him) that he said: "The trial that strikes like heated stones (al-radf) has come to you; the black and dark trial has come to you. Indeed, the trial has periods of pause and periods of surging. So whoever among you is able to die during its periods of pause, let him do so."
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Soon there will be a trial in which people will fight one another over the slogans of Jahiliyyah (pre-Islamic ignorance); those killed in such fighting will be in the Fire."
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he said: "O people! A trial like pieces of the dark night is about to overshadow you. The one most saved in it (or he said: from it) will be a man who owns sheep and lives on the milk of his flock, or a man beyond the frontier pass holding the reins of his horse and eating from (the earnings of) his sword (jihad)."
The chain of this hadith is authentic (sahih), but the two Shaykhs (Bukhari and Muslim) did not record it.