The Prophet (PBUH&HF) said: "Even if the entire duration of the world's existence has already been exhausted and only one day is left (before the day of judgment), Allah will expand that day to such a length of time, as to accommodate the kingdom of a person from my Ahlul-Bayt who will be called by my name. He will fill out the earth with peace and justice as it will have been full of injustice and tyranny (by then)."
Sunni References:
Sahih al-Tirmidhi, v2, p86, v9, pp 74-75
Sunan Abu Dawud, v2, p7
Musnad Ahmad Ibn Hanbal, v1, pp 84,376; V3, p63
al-Mustadrak ala al-Sahihayn, by al-Hakim, v4, p557
Jami' al-Saghir, by al-Suyuti, pp 2,160
al-Urful Wardi, by al-Suyuti, p2
al-Majma', by al-Tabarani, p217
Tahdhib al-Tahdhib, by Ibn Hajar al-Asqalani, v9, p144
Fat'h al-Bari fi Sharh Sahih al-Bukhari, by Ibn Hajar Asqalani, v7, p305
al-Sawa'iq al-Muhriqah, by Ibn Hajar al-Haythami, Ch. 11, section 1, p249
al-Tathkirah, by al-Qurtubi, p617
al-Hawi, by al-Suyuti, v2, pp 165-166
Sharh al-Mawahib al-Ladunniyyah, by al-Zurqani, v5, p348
Fat'h al-Mugheeth, by al-Sakhawi, v3, p41
Kanz al-Ummal, v7 P186
Iqd al-Durar Fi Akhbar al-Mahdi al-Muntadhar, v12, Ch. 1,
al-Bayan fi Akhbar Sahib al-Zaman, By Ganji al-Shafi'i, Ch. 12
al-Fusool al-Muhimmah, by Ibn Sabbagh al-Maliki, Ch. 12
Arjahul Matalib, by Ubaidallah Hindi al-Hanafi, p380
Muqaddimah, by Ibn Khaldoon, p266
and also in the works of Ibn Habban, Abu Nua'ym, Ibn Asakir, etc.
These six books are:
Sahih al-Bukhari
Sahih Muslim
Sahih al-Tirmidhi
Sahih al-Nisa'i
Sunan Ibn Majah
Sunan Abu Dawud
Also:
The Prophet (PBUH&HF) said: "al-Mahdi is one of us, the members of the household (Ahlul-Bayt)."
Sunni reference: Sunan Ibn Majah, v2, Tradition #4085
It is evident from the above traditions that Imam Al-Mahdi (AS) is from the Ahlul-Bayt of Prophet Muhammad(SAW), so he can not be Jesus (the Messiah; al-Maseeh). Thus, al-Mahdi and Messiah are two different personalities but they come at the same time, al-Mahdi as Imam and Jesus as his follower. The following tradition clearly mentions that Imam al-Mahdi is one of descendants of the daughter of Prophet Muhammad (PBUH&HF):
The Prophet (PBUH&HF) said: The Mahdi will be of my family, of the descendants of Fatimah (the Prophet's daughter).
Sunni references:
Sunan Abu Dawud, English version, Ch. 36, Tradition #4271 (narrated by Umm Salama, the wife of the Prophet)
Sunan Ibn Majah, v2, Tradition #4086
al-Nisa'i and al-Bayhaqi, and others as quoted in:
al-Sawa'iq al-Muhriqah, by Ibn Hajar al-Haythami, Ch. 11, section 1, p249
Also:
The Prophet (PBUH&HF) said: "We the children of Abd al-Muttalib are the Masters of the inhabitants of the heaven: Myself, Hamza (RA), Ali (AS), Ja'far Ibn Abi Talib (RA), al-Hasan (AS), al-Husain (AS), and al-Mahdi (AS)."
Sunni references:
Sunan Ibn Majah, v2, Tradition #4087
al-Mustadrak, by al-Hakim, on the authority of Anas Ibn Malik
al-Daylami
al-Sawa'iq al-Muhriqah, by Ibn Hajar al-Haythami, Ch. 11, section 1, p245
The Prophet (PBUH&HF) said: "The Mahdi will appear in my Ummah. He will appear for a minimum of 7 or a maximum of 9 years; at that time, my Ummah will experience a bountiful favor like never before. It shall have a great abundance of food, of which it need not save anything, and the wealth at that time is in great quantities, such that if a man asks the Mahdi to give him some, and the Mahdi (AS) will say: Here! Take!"
Sunni reference: Sunan Ibn Majah, v2, Tradition #5083
Remark: According to Shi'i sources, the Government of Peace and equality that Imam al-Mahdi will establish will last hundreds of years with no rival, and then the day of Judgment will commence. What is mentioned in the above tradition as 7 or 9 years is the length of time that Imam al-Mahdi (AS) will fight to conquer the world when he starts his mission.
The Prophet (PBUH&HF) said: "We (I and my family) are members of a household that Allah (SWT) 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."
Sunni references:
Sunan Ibn Majah, v2, Tradition #4082,
The History Tabari
al-Sawa'iq al-Muhriqah, by Ibn Hajar, Ch. 11, section 1, pp 250-251
Also:
The Messenger of Allah said: "The world will not perish until a man among the Arabs appears whose name matches my name."
Sunni reference: Sahih al-Tirmidhi, v9, p74
Sunni References:
Sahih al-Tirmidhi, v2, p86, v9, pp 74-75
Sunan Abu Dawud, v2, p7
Musnad Ahmad Ibn Hanbal, v1, pp 84,376; V3, p63
al-Mustadrak ala al-Sahihayn, by al-Hakim, v4, p557
Jami' al-Saghir, by al-Suyuti, pp 2,160
al-Urful Wardi, by al-Suyuti, p2
al-Majma', by al-Tabarani, p217
Tahdhib al-Tahdhib, by Ibn Hajar al-Asqalani, v9, p144
Fat'h al-Bari fi Sharh Sahih al-Bukhari, by Ibn Hajar Asqalani, v7, p305
al-Sawa'iq al-Muhriqah, by Ibn Hajar al-Haythami, Ch. 11, section 1, p249
al-Tathkirah, by al-Qurtubi, p617
al-Hawi, by al-Suyuti, v2, pp 165-166
Sharh al-Mawahib al-Ladunniyyah, by al-Zurqani, v5, p348
Fat'h al-Mugheeth, by al-Sakhawi, v3, p41
Kanz al-Ummal, v7 P186
Iqd al-Durar Fi Akhbar al-Mahdi al-Muntadhar, v12, Ch. 1,
al-Bayan fi Akhbar Sahib al-Zaman, By Ganji al-Shafi'i, Ch. 12
al-Fusool al-Muhimmah, by Ibn Sabbagh al-Maliki, Ch. 12
Arjahul Matalib, by Ubaidallah Hindi al-Hanafi, p380
Muqaddimah, by Ibn Khaldoon, p266
and also in the works of Ibn Habban, Abu Nua'ym, Ibn Asakir, etc.
These six books are:
Sahih al-Bukhari
Sahih Muslim
Sahih al-Tirmidhi
Sahih al-Nisa'i
Sunan Ibn Majah
Sunan Abu Dawud
Also:
The Prophet (PBUH&HF) said: "al-Mahdi is one of us, the members of the household (Ahlul-Bayt)."
Sunni reference: Sunan Ibn Majah, v2, Tradition #4085
It is evident from the above traditions that Imam Al-Mahdi (AS) is from the Ahlul-Bayt of Prophet Muhammad(SAW), so he can not be Jesus (the Messiah; al-Maseeh). Thus, al-Mahdi and Messiah are two different personalities but they come at the same time, al-Mahdi as Imam and Jesus as his follower. The following tradition clearly mentions that Imam al-Mahdi is one of descendants of the daughter of Prophet Muhammad (PBUH&HF):
The Prophet (PBUH&HF) said: The Mahdi will be of my family, of the descendants of Fatimah (the Prophet's daughter).
Sunni references:
Sunan Abu Dawud, English version, Ch. 36, Tradition #4271 (narrated by Umm Salama, the wife of the Prophet)
Sunan Ibn Majah, v2, Tradition #4086
al-Nisa'i and al-Bayhaqi, and others as quoted in:
al-Sawa'iq al-Muhriqah, by Ibn Hajar al-Haythami, Ch. 11, section 1, p249
Also:
The Prophet (PBUH&HF) said: "We the children of Abd al-Muttalib are the Masters of the inhabitants of the heaven: Myself, Hamza (RA), Ali (AS), Ja'far Ibn Abi Talib (RA), al-Hasan (AS), al-Husain (AS), and al-Mahdi (AS)."
Sunni references:
Sunan Ibn Majah, v2, Tradition #4087
al-Mustadrak, by al-Hakim, on the authority of Anas Ibn Malik
al-Daylami
al-Sawa'iq al-Muhriqah, by Ibn Hajar al-Haythami, Ch. 11, section 1, p245
The Prophet (PBUH&HF) said: "The Mahdi will appear in my Ummah. He will appear for a minimum of 7 or a maximum of 9 years; at that time, my Ummah will experience a bountiful favor like never before. It shall have a great abundance of food, of which it need not save anything, and the wealth at that time is in great quantities, such that if a man asks the Mahdi to give him some, and the Mahdi (AS) will say: Here! Take!"
Sunni reference: Sunan Ibn Majah, v2, Tradition #5083
Remark: According to Shi'i sources, the Government of Peace and equality that Imam al-Mahdi will establish will last hundreds of years with no rival, and then the day of Judgment will commence. What is mentioned in the above tradition as 7 or 9 years is the length of time that Imam al-Mahdi (AS) will fight to conquer the world when he starts his mission.
The Prophet (PBUH&HF) said: "We (I and my family) are members of a household that Allah (SWT) 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."
Sunni references:
Sunan Ibn Majah, v2, Tradition #4082,
The History Tabari
al-Sawa'iq al-Muhriqah, by Ibn Hajar, Ch. 11, section 1, pp 250-251
Also:
The Messenger of Allah said: "The world will not perish until a man among the Arabs appears whose name matches my name."
Sunni reference: Sahih al-Tirmidhi, v9, p74