Our Prophet (saas) has provided detailed information about Hazrat Mahdi (as). He has provided hundreds of signs comprehensively imparting the glad tidings of Hazrat Mahdi’s (as) coming, has flawlessly described Hazrat Mahdi’s (as) physical characteristics in astonishing detail and set out his moral values right down to the finest detail. On the basis of the hadiths of our Prophet (saas), great Islamic scholars have also said, in wise language and in a manner that everyone can easily understand, that Hazrat Mahdi (as) will appear in Hijri 1400, establish the unity of the Islamic world and be instrumental, together with the Prophet Jesus (as), in the global dominion of the moral values of Islam. Hazrat Mahdi (as) is a person appointed by Allah in destiny. Sincere believers can recognize Hazrat Mahdi (as) by evaluating the events they see and witness through their own consciences, in other words, through the light of faith. But it is certainly incompatible with the moral values of the Qur’an to say that this person is Hazrat Mahdi (as). All we can do is when, by Allah’s leave, the moral values of Islam rule the world and the Prophet Jesus (as) prays behind this holy individual, to say, “Allah knows the truth, this person is Hazrat Mahdi (as).” It is therefore incompatible with the Qur’an and the Sunna to make deductions along the lines of “I dreamed that such and such a person is the Mahdi, so he must be the Mahdi.”

First of all, it needs to be made clear that our Prophet (saas) has described the situation of those who falsely claim to have dreamed of something:
 

Ibni Umar relates:
The greatest lie is for someone to say he had a dream that he did not. (Bukhari, Tabir: 45, Musnad 2:96, 119; The translation based on Fays al-Qadir, the compilation by Suyuti)
 

For someone to maintain that anyone he saw in a dream is the Mahdi is equivalent to declaring that person to be a false Mahdi. And the appearance of false mahdis, false prophets and false messiahs is one of the portents of the coming of Hazrat Mahdi (as). This is described as follows in the hadiths:
 

The Day of Reckoning will not take place until the sending of some 30 liars, each of whom claims to be the messenger of Allah. (Tirmidhi, Fitan 43; Abu Dawud, Melahim 16)

The coming of 60 liars claiming to be sent as Messengers BY Allah, the One God. (Al-Muttaqi al-Hindi, Al-Burhan fi Alamat al-Mahdi Akhir az-Zaman, p. 36)
 

The citing of different figures, 30 or 60, in the hadiths shows that there will be a large number of false mahdis and prophets in the End Times.
False prophets are also referred to in the Qur’an. One verse on the subject reads:
 

Who could do greater wrong than someone who invents lies against Allah or denies His Signs, or who says, ‘It has been revealed to me,’ when nothing has been revealed to him, or someone who says, ‘I will send down the same as Allah has sent down’? If you could only see the wrongdoers in the throes of death when the angels are stretching out their hands, saying, ‘Disgorge your own selves! Today you will be repaid with the punishment of humiliation for saying something other than the truth about Allah, and being arrogant about His Signs.’ (Surat al-An’am, 93)