The Shea and the Sunni traditionalists have narrated that the advent of Imam al-Mahdi (AS) will be rectified by Allah within just one night. In other words, its time is very unpredictable and depends on Allah's sudden choice of action and his advent will take place miraculously. The Sunnis have narrated from Muhammad Ibn Hanafiyya (RA) and Imam Ali (AS) that the Holy Prophet (PBUH&HF) said:
"al-Mahdi is of us Ahl-ul-Bayt (AS); no doubt, Allah will rectify his matter within a night." In some other traditions, the Imams (AS) stated that the time of the rising of al-Qa'im (AS) is like the time of the Hour of resurrection, which is completely unpredictable and is known only by Allah. The time of resurrection has not yet been decreed and Allah shall enforce it suddenly once He wills. Di'bil narrated:
Imam Ali Ibn Musa al-Ridha (AS) said, "The Imam after me is my son, Muhammad (AS), and after him is his son Ali (AS), and after Ali is his son al-Hassan (AS), and after al-Hassan is his son the Proof of Allah who shall stand (al-Hujjat al-Qa'im). He is awaited during his occultation and is obeyed during his manifestation. Even if there remains from the life of the world but a single day, Allah shall expand that day until he rises and fills the world with justice in the same way that it was filled with tyranny and injustice. But when? As for news of the time (of reappearance),
indeed my father told me having heard it from his father who heard it from his ancestors who heard it from Ali (AS) that it was asked from the Prophet (PBUH&HF), 'O the Apostle of Allah! When will al-Qa'im from your offspring appear? He said, 'His similitude is the similitude of the Hour (of resurrection). None but He shall manifest it at its time. It is heavy for the heavens and the earth. It will not come to you unless suddenly. (7:187)'" Allah stated in Qur’an:
"They ask thee about the Hour - when will be its appointed time? Say, The knowledge thereof is with my Lord (alone). None but He shall manifest it at its time. It is heavy for the heavens and the earth. It will not come to you unless suddenly. They ask thee as if thou were eager in search thereof. Say, The knowledge thereof is with Allah (alone), but most men know not. (7:187)"
In fact, the traditions state that some of the Qur’anic terms and verses that apparently refer to the day of resurrection alternatively refer to the day of rising of al-Qa'im (AS). These terms include, "the hour (al-Saa'a)", "the hereafter (al-Akhira)", "the days of Allah (Ayyam Allah)", "the day of the religion (Yawm al-Din)", etc. One of the most important common specifications of both events is their sudden, unexpected, and miraculous manifestation.
Once Allah makes Badaa and creates His decree on the sudden advent of Imam al-Mahdi (AS), the first one who will become aware of it is the Imam (AS) himself through inspiration. Mufadhdhal Ibn Umar narrated:
On the commentary of verse, "Then, when it is knocked in Naqur (74:8)", Imam al-Sadiq (AS) said, "Certainly, of us will be an Imam who will be victorious and will be concealed. Once Allah, the Glorious, wills to manifest his affair, He shall impact his heart with a hint, and thereupon, he will emerge and will rise by the authority of Allah, the Glorious." Moreover, Abu Jarud narrated:
I said to Imam Muhammad al-Baqir (AS), "May I be sacrificed for you, inform me about the holder of this matter." The Imam (AS) replied, "He turns from the most fearful person to the most confident one overnight, and his program will be revealed to him in a matter of one night and one day." I asked, "Is this revealed to him?" The Imam (AS) replied, "O Aba Jarud, this is not the revelation of the prophethood. Rather, it will be a revelation similar to the one that He gave to Maryam, the daughter of Imran, to the mother of Moses, and to the honeybee. O Abu Jarud, the Qa'im of the family of Muhammad (PBUH&HF) is more honorable than Maryam, the mother of Moses, and the honeybee!"
imam mahdi (a.s)
The sudden change of the state of Imam Mahdi (AS) from the state of fear to the state of security, which is also pointed out in verse, "He will most certainly, after their fear, give them security in exchange (24:55)," shows that even the Imam (AS) does not know the time of his uprising until Allah initiates Badaa and makes it a knowable reality and permits his rising. Thus, like his followers, the Imam (AS) is himself an expectant. Of the titles that have been mentioned in the traditions for Imam al-Mahdi (AS) are: "the expected (al-Muntadhar)" and "the expectant (al-Muntadhir)".
All the above pieces of evidence, among others, prove that the time of the rising of Imam al-Mahdi (AS) is of suspended matters (Mawquf) and that his coming is very unpredictable and sudden.
This event will be one of the greatest manifestations of Allah's power, which will take place at the time that most people would consider it unfeasible.
Allah will suddenly make Badaa and will fully accommodate the Imam's advent within one night. Although the rising of al-Mahdi (AS) is in Allah's will, the time of his rising has not yet been decreed.
source : tebyan
