On the subject of the coming of the Prophet 'Isa (as) and the blessed Mahdi, there will be those who say, "Allah and His Messenger have promised us nothing more than an empty deception."
When the hypocrites and people with sickness in their hearts said, 'What Allah and His Messenger promised us was mere delusion'." (Surat al-Ahzab, 12)
In the Qur'an, Allah tells us that there will be people who say, "What Allah and His Messenger promised us was mere delusion." In the indicated meaning, this verse refers to the situation of those people who have lost hope of the coming of the Prophet 'Isa (as) and the blessed Mahdi. These people "deny the coming of the Prophet 'Isa (as) and the blessed Mahdi," which the Prophet (saas) reveals in the hadith, and they claim that the Prophet's (saas) words on this subject are supposedly "unfounded." Many writings appear in many places today, saying that the Prophet 'Isa (as) and the Mahdi will not be coming and, even more important, even people known as Islamic scholars issue statements along those same lines.
The truth of the matter is, however, that the fact that these people believe that "the coming of the Prophet 'Isa (as) and the Mahdi is untrue" and a supposedly "empty promise" is one of the things that our Prophet (saas) has promised us will happen. Because one of the portents of the End Times in the hadiths of our Prophet (saas) that the coming of the Prophet 'Isa (as) and the Mahdi is close at hand is the widespread nature of words to the effect that "The Mahdi will not come and there is no such person as the Mahdi." Some of the hadith on the subject read:
"Allah will send the Mahdi when people have despaired and say 'THERE IS NO SUCH PERSON AS THE MAHDI'." 1
"... THE MAHDI WILL COME, with the standard of the Messenger of Allah, WHEN HOPE OF HIS APPEARANCE HAS BEEN ABANDONED, and when scourges rain down on people's heads... " 2
... His (the Mahdi's) coming will be at a time of hopelessness and despair. 3
He (the Mahdi) will appear when people have lost all hope of his coming! How fortunate those who live in his time and help him will be! Woe to those who harbor enmity toward him, to those who oppose him and his commands, and to his enemies! 4
Dawud ibn Kathir Riqqi says: I asked Imam Abu Abdullah: ... This coming (of the Mahdi) is taking so long that our hearts have shrunk and we are dying from profound sorrow. And he said, "That appearance will take place when people are even more despairing and when sorrow is even greater." 5
This period, in which the portents of the End Times are taking place one after the other, shows that the return of the Prophet 'Isa (as) and the appearance of the Mahdi are close at hand. By Allah's leave, these two holy personages will appear just as described in the hadiths of our Prophet (saas) and will cause Islamic moral values to prevail across the world.
1 Ali ibn Husamaddin al-Muttaqi, Al-Burhan fi Alamat al-Mahdi Akhir al-Zaman, p. 55