Imam Mahadi is a descendent of Hassan

The name of the Mahadi as translated by this commentator need not be
Muhammad bin Abdullah, the usual full name of Prophet Muhammad. What
is said in the hadith is that the name is LIKE Prophet Muhammad. The
true name of Prophet Muhammad is not Muhammad but Ahmad.
Descendents of Hassan bin Ali bin Ahmad, call themselves Sharif.
Descendents of Hussin call themselves Syed. In Sabah, we only have
people who claim to be Sharif, which means that they are descendents
of Hassan.
Many people in Sabah have the names of Ahmad, and they could be
descendents of Hassan as well, just like my father. In my father's
family, he is the only one called Ahmad, and many people claim that he
is descended from a Sharif family. Many other people can be called
Ahmad and descendents of Prophet Muhammad as well, in Sabah. What
makes matters worse is that, I am also called Ahmad by Westerners who
call me by my father's name. I have 6 other siblings.
Is it possible that our ancestors are aware of this hadith and named
their children Ahmad or Muhammad in order to be honoured as Mahadi? We
are encouraged to name our children with the name of Muhammad in
front. That is why many Malaysians will have their names with Muhammad
in front.
http://www.topix.com/forum/world/brunei/T4QB7MFN31HB4G3TG
Kitab-kitab tersebut menerangkan bahawa nama Al-Mahdi ialah Muhammad
bin Abdullah sementara gelarannya pula ialah Abu Abdullah. Menurut
riwayat yang sah Al-Mahdi adalah dari keturunan Sayidina Hassan bin
Ali. Sesungguhnya telah tsabit bahawa Al-Mahdi adalah keturunan Hassan
bin Ali sebagaimana yang tersebut di dalam hadits sahih yang
diriwayatkan oleh Al-Imam Abu Daud dalam Sunannya,
"Telah berkata Ali sambil memandang puteranya ­Hassan," Sesungguhnya
Puteraku ini ialah sayid sebagaimana yang telah dinamakan oleh Nabi SA
W. Dari keturunannya akan lahir seorang lelaki yang namanya seperti
nama Nabi kamu, menyerupai baginda dalam perangai dan tidak menyerupai
baginda dalam rupa dan bentuk."

http://www.searchtruth.com/book_display.php?book=36&translator=3
4276
Narrated Ali ibn AbuTalib: AbuIshaq told that Ali looked at his son
al-Hasan and said: This son of mine is a sayyid (chief) as named by
the Prophet (peace_be_upon_him), and from his loins will come forth a
man who will be called by the name of your Prophet (peace_be_upon_him)
and resemble him in conduct but not in appearance. He then mentioned
the story about his filling the earth with justice.