Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Volume 3, Page 142, Question No.1 of Fatwa No.7664
Question: Who is the Mahdee, and what are the signs of the [Last] Hour?
Response: [He is] a man from the family of the Prophet (sal-Allaahu ‘alayhi wa sallam), who will appear before the descending of ‘Eesaa (Jesus) the son of Mary (sal-Allaahu ‘alayhi wa sallam) and he will invite [the ummah] to Islaam. And Allaah will establish the proof by way of him, and many people will be guided by him.
If you want further [information] regarding this, then read what Ibn Katheer has written about him in his book «al-Bidaayah wan-Nihaayah».
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.