AL-MAHDI المهدي
Lit. ‘The Directed One,” hence, “who is fit to direct others, Guide, Leader.” A. ruler who shall in the last days appear upon the earth. According to the Shi’ahs, he has already appeared in the person of Muhammad Abu ‘1-Qasim, the twelfth Imam, who is believed to be concealed in some secret place until the day of his manifestation before the end of the world. But the Sunnis say he has not yet appeared. In the history of Islamism, there are numerous instances of impostors having assumed the character of this mysterious personage, amongst others, Saiyad Ahmad, who fought against the Sikhs on the North-West frontier of the Punjab, AD. 1826, and still who has claimed to be al-Mahdi in Sudan in Egypt.
The sayings of the Prophet on the subject, according to al-Bukhari and other traditionists are as follows :—
“The world will not come to an end until a man of my tribe and of my name shall be master of Arabia.”
“When you see black ensigns coming from the direction of Khorosan, then join them, for the Imam of God will be with the standards, whose name is al-Mahdi.”
“The Mahdi will be descended from me, he will be a man with an open countenance and with a high nose. He will fill the earth with equity and justice, even as it has been filled with tyranny and oppression, and be will reign over the earth seven years.”
Quarrelling and disputation shall exist amongst men, and than shall a man of the people of al-Madinah come forth, and shall go from al-Madinah to Makkah, and the people of Makkah shall make him Imam. Then shall the ruler of Syria send up army against the Mahdi, but the Syrian army shall perish by an earthquake near Bada’, between al-Madinah and Makkah. And when the people shall see this, the Abdal [ABDAL] will come from Syria, and also a multitude from al-‘Iraq. After this an enemy to the Mahdi sha1l arise from the Quraish tribe, whose uncles shall be of the tribe of Kalb, and this man shall send an array against the Mahdi. The Mahdi shall rule according to the examp1e of your Prophet, and shall give strength and stability to Islam. He shall reign for seven years, and than die.”
“There shall be much rain in the days of the Mahdi and the inhabitants both of heaven and earth shall he pleased with him. Men’s lives shall pass so pleasantly, that they will wish even time dead were alive again.” (Mishkatu’l-Masanih, book xxiii. ch. 3.)
According to Shi’ah traditions, Muhammad is related to have said “O ye people! I am the Prophet and ‘Ali is my heir, and from us will descend al-Mahdi, the seal (i.e. the last) of the Imams, who will conquer all religion; and take vengeance on the wicked. He will take fortresses and will destroy them and slay every tribe of idolaters and he will avenge the deaths of the martyrs of God. He will be the champion of the Faith, and a drawer of water at the fountain of divine knowledge. He will reward merit and requite every fool according to his fo1ly. He will he the approved and chosen of God, and the heir of all knowledge. He will be the valiant in doing right, and one to whom the Most High has entrusted Islam. . . O ye people, I have explained to you, and ‘Ali also will make you understand it.” (Hiyatu ‘l-Qulub, Merrick’s ed., p. 342.)
It is probable that it is from these traditions that the opinion became current amongst the Christians that the Muslims expected their Prophet would rise again.

Based on Hughes, Dictionary of Islam