Al-Islam.org claim Sunni Scholars affirmed the 12 imam as Mahdi

[Aba AbdAllah]

Many Sunni scholars did indeed say that the 12th Imam is Mahdi, and the 4th and 5th Imam are Ali and Hassan.

So we agree that out of the 12 imams 3 of them....

The  ones mentioned are most those associated with Sufism. The Sufis themselves say their beliefs and practices are not binding on the Ummah. Also, the main Sufi figure who claimed he was a representative of the 12th Imam was Al Mansoor al Hajjaj. When Al Mansoor brought the news to Shaykh Saduq, Shaykh Saduq joined forces with Anti Sufi Sunnis, and got him killed. So again the proofs are unconvincing.

Could you please provide source for this? and is the reference available online?

[Rationalist]

Here is a Sufi link.
https://ahmedamiruddin.wordpress.com/2012/04/20/reflecting-on-the-execution-of-abu-l-mughith-husayn-ibn-man%E1%B9%A3ur-al-%E1%B8%A5allaj/

12er Shia link.
http://www.shiavault.com/books/the-life-of-imam-al-mahdipeace-be-upon-him/chapters/18-the-major-occultation