حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَحْمَدُ بْنُ عَبْدِ الْمَلِكِ، حَدَّثَنَا أَبُو الْمَلِيحِ الرَّقِّيُّ، عَنْ زِيَادِ بْنِ بَيَانٍ، عَنْ عَلِيِّ بْنِ نُفَيْلٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، قَالَ كُنَّا عِنْدَ أُمِّ سَلَمَةَ فَتَذَاكَرْنَا الْمَهْدِيَّ فَقَالَتْ سَمِعْتُ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ يَقُولُ ‏"‏ الْمَهْدِيُّ مِنْ وَلَدِ فَاطِمَةَ ‏"‏ ‏.‏

It was narrated that Sa'eed bin Musayyab said: "We were with Umm Salamah and we were discussing Mahdi. She said: 'I heard the Messenger of Allah (PBUH) say: "Mahdi will be one of the descendents of Fatimah." Translation Not Available

Book Ref: Sunan Ibn Majah Book 36 Hadith 4086
Web Ref:  Sunan Ibn Majah Vol 5 Book 36 Hadith 4086