Mahdi Will Rule For 7 or 9 Years

The Prophet (sawa) 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 bountiful favors 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! (Sunan Ibn Majah volume 2 tradition no. 5083)

The Prophet (sawa) said, We (I and my family) are members of a household that Allah has chosen for them the life of the Hereafter over the life of this world; and the members of my household (Ahle 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 (Ahle 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 vicegerent of Allah (Khalifatullah) Mahdi.”

References:

Sunan Ibn Majah, volume 2 tradition no. 4082
Tarikh by Tabari
al-Sawa’iq al-Muhriqah, by Ibn Hajar chapter 11 section 1 pages 250-251

Holy Prophet (sawa) said, “The Mahdi is from me. He has a broad forehead and protracted nose. He will fill the earth with equality and justice as it will be filled with tyranny and injustice. He will rule for seven years.” (Faizul Qadeer Sharhe Jaame-us-Sageer by Mohammed Abdur Rauf bin Taajul Aarfeen ibn Ali Ibne Zainul Abedeen volume 6 , tradition 9244)

Holy Prophet (sawa) said, “The Mahdi is from me. He has a broad forehead and protracted nose. He will fill the earth with equality and justice as it will be filled with tyranny and injustice. He will rule for seven years.” (Liwaaehul Anwaaarul Elaahiyyah by Shamsuddin Mohammed ibne Ahmed Ibne Salim volume 2)

Holy Prophet (sawa) said, “The Mahdi is from me. He has a broad forehead and protracted nose. He will fill the earth with equality and justice as it will be filled with tyranny and injustice. He will rule for seven years.” (Awnul Mabud Sharhe Sunane Abi Dawood by Mohammed Shamsud Haqul Azim, chapter Awwal Kitabul Mahdi tradition 4265)

Read more about Imam Mahdi in the Ahle Sunnah