I'm writing this document as a respond to requests from many Muslims and non-Muslims. I found many documents about this subject that contains a lot of false Hadeeths. This document is a result for a long research in evaluating every Hadeeth (true or false). Arabic version is also availavble.
The term "MAHDI" is a title meaning "The Guided one". Mahdi is a normal man who is going to follow the true Islam. His name will be Muhammad and his father name will be 'Abdullah. He is a descendant from Ali and Fatima (daughter of the prophet Muhammad (pbuh)) so he will be descendant from al-Hasan or al-Husain. Mahdi will be very just and his capital will be Damascus. Allah told us that Jews will master the world two times (we live now 1998 during the first one) and Mahdi will appear between those two periods and will rule through the last one. Mahdi is NOT a prophet but he is the final Rightly Guided Khalifa. Mahdi will lead Muslims to a great victory against the Christian Romans (i.e. All the white Europeans including the Americans). This great war is called al-Malhamah al-Kubrah or Armageddon. It will end up with a great victory to Muslims against Romans after six years. Muslims will take over their capital Rome (this can be any city). In the seventh year, the Anticrist will apear and a greater war will start between Jews and Muslims for 40 days (longer that usual days) and will end when Jesus (pbuh) will come and Muslims will kill all Jews. All people will convert into Islam. Peace will pervade the whole world.
As Muslims, we should remember that the prophecy about Mahdi is one that will come to pass. This prophecy, however, does not absolve the Muslim Ummah from its duty to strive in the cause of Allah, oppose injustice, and seek peace and betterment of human condition. Centuries have passes from the time of the holy Prophet and there is a good possibility that many more will expire before the advent of the Mahdi. Muslims who are negligent in their duty hoping for a savior are committing a grave mistake and are not following the divine decrees ordained in Quran or taught by the Prophet Muhammad (pbuh).
Correct Hadeeths (AHadeeth SaHiHa)
Narrated Jabir ibn Samurah:
The Prophet (pbuh) said: The religion will continue to be established till there are twelve caliphs (Khalifas) over you, and the whole community will agree on each of them. I then heard from the Prophet (pbuh) some remarks which I could not understand. I asked my father: What is he saying: He said: all of them will belong to Quraysh.
Disagreement will occur at the death of a caliph (khalifa) and a man of the people of Medina (Madina) will come flying forth to Mecca (Makka). Some of the people of Mecca will come to him, bring him out against his will and swear allegiance to him between the Corner and the Maqam. An expeditionary force will then be sent against him from Syria (Al-Sham) but will be swallowed up in the desert between Mecca and Medina. When the people see that, the eminent saints (Al-Abdal) of Syria and the best people of Iraq will come to him and swear allegiance to him between the Corner and the Maqam.
Then there will arise a man of Quraysh whose maternal uncles belong to Kalb and send against them an expeditionary force which will be overcome by them, and that is the expedition of Kalb. Disappointed will be the one who does not receive the booty of Kalb. He will divide the property, and will govern the people by the Sunnah of their Prophet (pbuh) and establish Islam on Earth. He will remain seven years, then die, and the Muslims will pray over him.
An army would attack this House in order to fight against the inhabitants of this House and when it would be at the plain ground the ranks in the centre of the army would be sunk and the vanguard would call the rear flanks of the army and they would also be sunk and no flank would be left except some people who would go to inform them (their kith and kin).
Narrated Mustawrid al-Qurashi: I heard Allah's Apostle (pbuh) said: The Last Hour would come (when) the Romans would form a majority amongst people (This is exactly the situation today since Europeans and Americans are the largest group). Amr said to him (Mustawrid al-Qurashi): See what you are saying? He said: I say what I heard from Allah's Apostle (pbuh) Thereupon he said: If you say that, it is a fact for they have four qualities. (1) They have the patience to undergo a trial and (2) immediately restore themselves to sanity after trouble and (3) attack again after flight. (4) They (have the quality) of being good to the destitute and the orphans, to the weak and, fifthly, the good quality in them is that (5) they put resistance against the oppression of kings.
"You will invade the Arabian Peninsula and Allah will grant it (to you). Then (you will invade) Persia and Allah will grant it (to you). Then, you will invade Rome (the Romans) and Allah will grant it (to you). Then, you will invade The Dajjal (and Jews) and Allah will grant him (to you)." (So the Dajjal would not appear until Rome is conquered.)
The Prophet (pbuh) said: The time between the great war and the conquest of the city (Constantinople) will be six years, and the Dajjal (Antichrist) will come forth in the seventh.
AbuNadrah reported: We were in the accompany of Jabir and he said: It may happen that the people of Iraq may not send their qafiz and dirhams (their measures of food-stuff and their money). We said: Who would be responsible for it? He said: The non-Arabs would prevent them (this is exactly what happens today). He again said: There is the possibility that the people of Syria may not send their dinar and mudd. We said: Who would be responsible for it? He said: This prevention would be made by the Romans (i.e. All the white Europeans including the Americans).
He (Jabir ibn Abdullah) kept quiet for a while and then reported Allah's Apostle (pbuh) having said: There would be a caliph in the last (period) of my Ummah who would freely give handfuls of wealth to the people without counting it.
I said to AbuNadrah and AbulAla: Do you mean Umar bin AbdulAziz? They said: No. (he would be Imam Mahdi)
Good Hadeeths (AHadeeth Hasana)
If only one day of this world remained. Allah would lengthen that day, till He raised up in it a man who belongs to me or to my family whose father's name is the same as my father's, who will fill the earth with equity and justice as it has been filled with oppression and tyranny. (Abu-Dawud)
The Mahdi will be of my family, of the descendants of Fatimah (the daughter of the Prophet (pbuh) who married Ali and begot Hasan and Hussein). (Abu-Dawud)
The Mahdi will be of my stock, and will have a broad forehead a prominent nose. He will fill the earth will equity and justice as it was filled with oppression and tyranny, and he will rule for seven years. (Abu-Dawud)
Week Hadeeths (AHadeeth Da3ifa, probably they were fabricated)
AbuIshaq told that Ali looked at his son al-Hasan and said: This son of mine is a sayyid (chief) as named by the Prophet (pbuh), and from his loins will come forth a man who will be called by the name of your Prophet (pbuh) and resemble him in conduct but not in appearance. He then mentioned the story about his filling the earth with justice. (Abu-Dawud)
Fabricated Hadeeths (AHadeeth MauDu3a)
A man called al-Harith ibn Harrath will come forth from Ma Wara an-Nahr (Middle Asia). His army will be led by a man called Mansur who will establish or consolidate things for Muhammad's family as Quraysh consolidated them for the Apostle of Allah (pbuh). Every believer must help him, or he said: respond to his sermons.
The Prophet (pbuh) said: "We (I and my family) are members of a household that Allah (pbuh) has chosen for them the life of the Hereafter over the life of this world; and the members of my household (Ahlul-Bayt) shall suffer a great affliction and they shall be forcefully expelled from their homes after my death; then there will come people from the East carrying black flags, and they will ask for some good to be given to them, but they shall be refused service; as such, they will wage war and emerge victorious, and will be offered that which they desired in the first place, but they will refuse to accept it till they pass it to a man from my family (Ahlul-Bayt) appears to fill the Earth with justice as it has been filled with corruption. So whoever reaches that (time) ought to come to them even if crawling on the ice/snow since among them is the Vice-regent of Allah (Khalifatullah) al-Mahdi."
(Armies carrying) black flags will come from Khurasaan (east of Iran). No power will be able to stop them and they will finally reach Eelia' (Baitul Maqdas) where they will erect their flags.
"There will be many armies after me. You must join that army which will come from Khurasaan." (Ibn Adi)
The Prophet (pbuh) said: The greatest war, the conquest of Constantinople and the coming forth of the Dajjal (Antichrist) will take place within a period of seven months. (Actually, it is seven years.)
"At the time when Nafs al-Zakiyya is killed a caller from the heaven will say: 'Your commander is so-and-so.' (announce Mahdi) Following it the Mahdi will emerge and fill the earth with justice and equity." (Ibn Tawus, Kitab al-malahim wa al-fitan, P. 179)