Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Volume 3, Page 141, Fatwa No.2844
Question: I request you provide me with a fatwa as to the authenticity and existence of the Mahdee about whom it is said he is on the Earth. And are there any authentic ahaadeeth which mention him? May Allaah reward you.
Response: The authentic ahaadeeth which mention the appearance of the Mahdee are many, and they are mentioned in a number of narrations from the Imaams of Hadeeth. And a group from the people of knowledge mention that they are mutawaatir (that which is narrated by such a large number of people that it is impossible that they have invented a lie) in meaning, from amongst them are Abul-Hasan al-Aajuree who is from the scholars of the [hijree] fourth century and the noble scholar as-Safaareenee in his book «Lawaami’ al-Anwaar al-Bahiyyah», and the noble scholar ash-Showkaanee in his treatise «at-Towdeeh fee tawaatur Ahaadeeth al-Mahdee wad-Dajjaal wal-Maseeh».
And he (the Mahdee) has many well-known signs which are mentioned in the ahaadeeth, [of which] the most important are:
«That he will fill the Earth with uprightness and justice after it had been filled with injustice and oppression».
And it is not permissible for anyone to believe that such and such the son of such and such is the Mahdee, until the signs which the Prophet (sal-Allaahu ‘alayhi wa sallam) mentioned in the authentic ahaadeeth are prevalent, the most important of which we have mentioned:
«That he will fill the Earth with uprightness and justice…», the hadeeth.
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet (sal-Allaahu ‘alayhi wa sallam) and his family and his companions.