Hadhrat Umme Salmah (R.A.) narrates that Rasulullah (Sallallahu Alayhi Wasallam) said, " After the death of a Ruler there will be some dispute between the people. At that time a citizen of Madina will flee (from Madinah) and go to Makkah. While in Makkah, certain people will approach him between Hajrul Aswad and Maqaame Ibraheem, and forcefully pledge their allegiance to him.
Thereafter a huge army will proceed from Syria to attack him but when they will be at Baida, which is between Makkah and Madina, they will be swallowed into the ground.
On seeing this, the Abdaals of Shaam as well as large numbers of people from Iraq will come to him and pledge their allegiance to him. Then a person from the Quraish, whose uncle will be from the Bani Kalb tribe will send an army to attack him, only to be overpowered, by the will of Allah. This (defeated) army will be that of the Bani Kalb. Unfortunate indeed is he who does not receive a share from the booty of the Kalb. This person (Imam Mahdi) will distribute the spoils of war after the battle. He will lead the people according to the Sunnat and during his reign Islam will spread throughout the world. He will remain till seven years (since his emergence). He will p*** away and the Muslims will perform his Janazah salaat." (Abu Dawood)
According to a Hadeeth, Sayyidena Eesa (A.S.) will lead the Janaazah of Imam Mahdi (A.S.).
While the people will be pledging their allegiance to Imaam Mahdi, a voice from the unseen will call out:
"This is the representative of Allah,
The Mahdi, listen to him and obey him"
This announcement which will be heard by all those present will establish his authenticity. Another sign which will indicate the authenticity of Imaam Mahdi wil be that in the Ramadhaan prior to his emergence an eclipse of the sun and moon will occur.
Hadhrat Abu Umamah (R.A.) says that Rasulullah (Sallallahu Alayhi Wasallam) said: "There will be four peace agreements between you and the Romans. The fourth agreement will be mediated through a person who will be from the progeny of Hadhrat Haroon (A.S.) and will be upheld for seven years."
The people asked: "O Rasulullah (Sallallahu Alayhi Wasallam), who will be the Imaam of the people at the time?"
Rasulullah (Sallallahu Alayhi Wasallam) said: "He will be from my progeny and will be forty years of age. His face will shine like a star and he will have a black spot on his left cheek. He will don two "Qutwaani" cloaks and will appear exactly as a person from the Bani Israeel..." (Tabrani)
According to hadith narrated by Abu Saeed Khudri (R.A.) Rasulullah (Sallallahu Alayhi Wasallam) said: "...(regarding the rule of Imaam Mahdi) the skies will rain down in abundance and the earth will yield forth its crop in abundance, and those alive will desire that those who have already p***ed away should have been alive to enjoy this prosperity..."
Hadhrat Buraidah (R.A.) says that Rasulullah (Sallallahu Alayhi Wasallam) said: "There will be many armies after me. You must join that army which will come from Khurasaan." (Ibn Adi)
Abu Hurairah (R.A.) says that Rasulullah (Sallallahu Alayhi Wasallam) said: "(Armies carrying) black flags will come from Khurasaan. No power will be able to stop them and they will finally reach Eela (Baitul Maqdas) where they will erect their flags."
from: "Signs of Qiyamah"
by Mohammed Ali Ibn Zubair Ali