Reference: Fataawa Islaamiyyah – Volume 1, Page 56
Question: What is your opinion about the appearance of the promised person, al-Mahdee?
Are there any ahaadeeth to verify this? I request clarification regarding this [matter]?
Response: There are numerous ahaadeeth which are reported by the leading authorities in the science of hadeeth verifying the advent of the expected Mahdee, the Dajjaal and the Messiah [Jesus (‘alayhis-salaam)]. Certain signs will precede his advance; the most significant of which is that he will make justice prevail on earth after the prevalence of injustice and tyranny. It is not permissible today for anyone to allege that a certain person is the Mahdee until his signs that the Prophet (sal-Allaahu ‘alayhi wa sallam) foretold have appeared such as the one mentioned above.
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.