Question Summary:
Is our Imam Mahdi the same person the Shias refer to as Imam Mahdi?

Question Detail:

Im from France and I have a problem on logging in the website, thus I cannot ask questions. I managed to subscribe but as I when to sign in it does not work so I may ask my question here :
Is the Mahdi mentionned in the Quran, related to the Imam Muhammed al Mahdi, the 12th missing chii imam the Chii are waiting for? The descriptions are very very similar and I was wondering if it was about the same person?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
There is no mention of Imam Mahdi in the Quran. However, Imam Mahdi is mentioned in many Ahadith. Consider the following Ahadith:
يَكُونُ فِي أُمَّتِي الْمَهْدِيُّ إِنْ قُصِرَ فَسَبْعٌ، وَإِلَّا فَتِسْعٌ، فَتَنْعَمُ فِيهِ أُمَّتِي نِعْمَةً، لَمْ يَنْعَمُوا مِثْلَهَا قَطُّ، تُؤْتَى أُكُلَهَا وَلَا تَدَّخِرُ مِنْهُمْ شَيْئًا، وَالْمَالُ يَوْمَئِذٍ كُدُوسٌ، فَيَقُومُ الرَّجُلُ، فَيَقُولُ: يَا مَهْدِيُّ أَعْطِنِي، فَيَقُولُ خُذْ
"The Mahdi will be among my nation. If he lives for a short period, it will be seven, and if he lives for a long period, it will be nine, during which my nation will enjoy a time of ease such as it has never enjoyed. The land will bring forth its yield and will not hold back anything, and wealth at that time will be piled up. A man will stand up and say: 'O Mahdi, give me!' He will say: 'Take.'"[1]
الْمَهْدِيُّ مِنِّي، أَجْلَى الْجَبْهَةِ، أَقْنَى الْأَنْفِ، يَمْلَأُ الْأَرْضَ قِسْطًا وَعَدْلًا، كَمَا مُلِئَتْ جَوْرًا وَظُلْمًا، يَمْلِكُ سَبْعَ سِنِينَ 
The Prophet (ﷺ) said: The Mahdi will be from me (my family), and will have a broad forehead, a prominent nose, he will fill the earth will equity and justice as it was filled with oppression and tyranny, and he will rule for seven years.[2]
Indeed, the Shias do believe in the very same Imam Mahdi as mentioned above. However, they hold some corrupt beliefs concerning Imam Mahdi. It is stated in their book, “Usool Kafi”:
رتبہ امامت برتر از نبوت است
“The position of Imamat is greater than that of Nubuwah/Prophethood.” [3]
Thus, they believe Imam Mahdi will be greater and hold a higher status than Rasulullah Sallallahu Alayhi Wasallam despite the fact that there is a consensus on Rasulullah Sallallahu Alayhi Wasallam being the greatest person on earth.
It is further mentioned in their book, “Haqq-ul-Yaqin” that Imam Mahdi will appear naked.[4] It is also mentioned that Imam Mahdi will initially kill all the Sunni scholars after his appearance.[5]
The Shias also believe that the current Quran in our possession is incomplete. Present day Shias feel uncomfortable with such a belief; whereas it is mentioned in “Usool Kafi”, along with their book, “Hazaar Tumhaare Das Hamaare”[6] that the real Qur’an lays within a cave with Imam Mahdi.[7]  
It should also be pointed out that the Shias believe in Taqiyya, which is the beliefof “holy lying”.[8] In such an instance, what is the point in discussing anything with Shias who believe in the concept of lies to propagate ones beliefs? Is the reality such that they are propagating and calling people towards their beliefs whilst the entire propagation may be a lie? Indeed, the entire discussion and propagation is baseless!
And Allah Ta’āla Knows Best
AbdulMannan Nizami
Student Darul Iftaa
Chicago, IL, USA
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net