Allah says in one of the Qur'anic verses as follows: 

{And with Him are the keys of the Ghaib (all that is hidden), none knows them but He. And He knows whatever there is in (or on) the earth and in the sea; not a leaf falls, but He knows it. There is not a grain in the darkness of the earth nor anything fresh or dry, but is written in a Clear Record.} (V.6:59) 

It means that Allah has bestowed on the humans some faculties so that they may have an access to the knowledge concerning the apparent on the physical plane; for instance eyes to sight, ears to listen, nose to smell, tongue to taste, hands to grope about, and intellect to understand. Then, the above faculties have been put at the disposal of a human being so that he may utilize them on his own accord; for instance, whenever he intends to see an object, he may open his eyes and whenever he does not intend to see it, he may close them. Other limbs may also be utilized in a similar manner. Human beings have been given the keys to have an access to the knowledge of the evident things. As the matter of doing and undoing a lock mainly depends on the will of its owner, similarly the act of gaining knowledge about the apparent things depends upon the will of a human being. 

Only Allah possesses the knowledge of Ghaib (unseen and hidden): Contrary to the above, it is beyond the authority of a human being to gain the knowledge of the unknown, as Allah Himself preserves the keys to it. No entity whatsoever (whether one of

the most prominent humans or one of the most eminent angels) has been given an authority to know about the unseen in a manner that they may exercise their own will to gain knowledge about the hidden matters. However, whenever Allah so wishes, He reveals a certain amount of information concerning the Unknown to someone. Giving information about the unknown solely depends on the Will of Allah and not on the desire of someone. On many occasions Allah's Prophet {Peace be upon Him} had a desire to gain knowledge about a certain thing or occurrence, which he could not know, but the same was revealed to him whenever Allah intended to do so. During the era of Prophethood, the hypocrites slandered `Aisha {May Allah have mercy on Her} which shocked the Prophet {Peace be upon Him} tremendously. He tried- to probe into the matter for -many days, but failed to ferret out the truth. And when Allah intended, the Prophet was informed through the process of revelation that the hypocrites are none but liars and the chastity of 'Aisha Siddiqah {May Allah have mercy on her} was verily beyond reproach. A Muslim monotheist must have a conviction that Allah preserves the keys to the treasures of the unknown with none but Himself and has appointed none as their treasurer. No one can stop Him if He Himself awards something to whomsoever He so wishes (by Himself unlocking one of His treasures). The one who claims to have the knowledge of Ghaib (unseen), is a liar:

We thus understand that anyone who claims to possess a certain art or knowledge enabling him to have a peep into the Ghaib, to reveal the past incidents and to adumbrate about the futuristic events, is an outright liar claiming godship. In case someone recognizes a Prophet, a saint, a jinn, an angel, an Imam, a man of piety, a religious preceptor, a martyr, an astrologer, a seer, a clairvoyant, a prestidigitator, a pundit, a ghost, or a fairy to be as such (having the knowledge of the unknown), such a person becomes a Mushrik, and he (rejects and negates) denies the contents of the above verses. Even if a certain prediction of an astronomer, by a sheer chance, happens to come true, it does not prove his knowledge of the unknown because most of their statements turn out to be incorrect. Hence we understand that it is beyond their capacity to have a knowledge of the Ghaib. A conjectural utterance may at times prove to be correct and at times incorrect. The same is also true in regard to making Prophecies, getting the things known through a Divine Inspiration, or resorting the Qur'anic verses to gain an insight into the future events. A revelation, however, is never incorrect and is not under their control. Allah reveals whatever He intends to, out of His Own Free Will. A revelation does not depend on the desire of anyone. Allah the Exalted says:

 

{Say: 'None in the heavens and the earth knows the Ghaib (unseen) except Allah, nor can they perceive when they shall be resurrected.}(V.27:65)

It means that no one has the capability to have an access to the knowledge of the Ghaib whether he is one of the most prestigious human beings or one of the most high-ranking angels. This fact may be corroborated by the evidence that the whole world knows about the advent of the Doomsday, but none of them knows as to when shall it occur! Had they been possessing the capability to gain knowledge of everything, they would have known the date of its advent also!

The matters of Ghaib (the unknown and unseen): Allah the Almighty says:

 

{Verily, Allah! With Him (alone) is the knowledge of the Hour, He sends down the rain, and knows that which is in the wombs. No person knows what he will earn tomorrow, and no person knows in what land he will die. Verily, Allah is All-Knower, All-Aware (of things.} (V.31:34)

It means that Allah Alone knows the matters of the Ghaib. While no one other than Him has the knowledge of the unseen. Nobody knows as to when shall the Doomsday occur, a news so much wide-spread and well-known among the people that they are almost certain about its occurrence, what about the matters like victory and defeat, health and sickness and (others like it) similar to it. No one knows about them either. These matters are neither well-known like the Doomsday nor are absolutely definite. Similarly, nobody knows when shall it start raining even though it has a definite season and it often rains during that season. Most of people do wish to know about it and had it been possible to know it beforehand, they would indeed have known about it. Then how could the people possibly know about the things which neither belong to a particular season nor are they of any public interest like someone's death and his life-span, being blessed with a child or not, being wealthy or impoverished, emerging victorious or facing an ignominy of defeat etc. No one knows as to whether a womb carries one or more than one child [1] , whether a fetus is a male one or a female one, complete or defective, beautiful or ugly, even though the physicians do narrate the reasons causing different formations and configurations, but they do not know about someone's particular case. In such a case, how could one possibly read the internal matters of a person like thoughts, intentions and the condition of one's Faith and hypocrisy. As long as one does not know as to what he himself shall be doing tomorrow, how could he know about the circumstances of others and since a man does not even have an inkling about the place of his death, how could he have a fore-knowledge about the day and time of his passing away. Be it as it may, no person or entity has the capability to learn about the future by exercising his own free will and choice except Allah. Hence it becomes known to us that the people who claim to have the knowledge of the unseen are none but liars. The so-called concepts and methods of learning about what is unseen like a Divine inspiration, soothsaying, foretelling by figures, astronomy, divination and casting lots are none but falsehood and are only Satanic tricks and illusions. Muslims should not be entangled with them and give them no credit at all. And if someone neither claims to possess the knowledge of the unseen nor claims to have the capability of knowing it by exercising his own free will but he only claims that a certain matter which Allah has informed him about, was beyond his control and capacity; and his own choice and will, had nothing to do with it; in this case there are both the possibilities, the man making such a statement, could either be truthful or a liar.

Do not call upon anyone but Allah: Allah says: 

{And who is more stray than one who calls (invokes) besides Allah, such as will not answer him till the Day of Resurrection, and who are (even) unaware of their calls (invocations) to them?} (V.46:5)

It means that the polytheists are an extremely idiotic bunch of people, who, by avoiding Allah (who possesses all authority and knowledge) invoke the other so-called deities who neither hear their invocations nor are capable of doing anything. Even if they keep calling them till the Doomsday, those (so-called) deities would not respond to their calls. Thus we may deduce that the people who call upon the men of piety from a certain distance by only requesting them to pray to Allah for them so that Allah may fulfill their wishes, also commit an act of Shirk even though they may not think it to be as such, since the prayer of fulfillment is eventually directed to Allah. But in fact, this act has become tainted with Shirk as a third person has been called upon with the belief that this person possesses the capability of hearing from far and near (if invoked), whereas it is a quality which is attributed to Allah Alone. Allah Himself says that they (deities etc.) are unaware of their calls (invocations) to them. They do not hear the invocations of a caller even if he keeps shouting (his invocations) until the Doomsday.

Allah Alone, possesses the power of benefit and inflicting harm: {Say (O Muhammad {Peace be upon Him}): “I possess no power of benefit or hurt to myself except as Allah wills. If I had the knowledge of the Ghaib (unseen), I should have secured for myself an abundance of wealth, and no evil should have touched me. I am but a warner, and a bringer of glad tidings unto people who believe.”}(V. 7: 188)

The Prophet {Peace be upon Him}is the leader of all the Prophets. Many miracles are ascribed to him and people learned the subtleties and nuances of religion from him. People acquired piety and virtuosity by following his prescribed path. Allah Himself I instructed him to give people an account of his helplessness making it clearly known to the people that he is neither capable of exercising any authority nor possesses any knowledge of the unseen. One can easily run a conjecture from the fact that as long as he does not even possess an authority to gain a certain advantage for himself or to ward off an evil from inflicting him, how could he benefit or harm someone else. Had he been having the knowledge of the unseen, he would have known about the results of a certain action beforehand even prior to undertaking it, and if he had a faintest premonition that the result of a certain action is going to be unfavorable, he would not have undertaken that action at all. The knowledge of the unseen is one of the Attributes of Allah and he is merely a Messenger. The mission of a Messenger is only confined to warning people about the dire consequences of bad actions and to give people glad tidings about virtuous deeds. This too benefits the ones who nurse such a Belief (Tauhid) in their hearts and the nurturing of such a Belief is also one of the Qualities of Allah.

The original assignment of the Prophets:

It becomes known to us that the greatness of the Prophets and saints epitomizes in the fact that they direct people to the path of Allah and give people information about whatever good and bad deeds they are themselves informed of. Allah has endowed their propagation with a quality of a convincing effectiveness. Many people are directed to the Right Path through their efforts. No such authority has been conferred on them that they should personally conduct and dispose off the worldly matters like causing death to someone, bless someone with a son or daughter, warding off an evil, fulfillment of one's wishes, crowning someone with success or destine someone to defeat, granting someone riches or making someone indigent and impoverished, turning someone into either a king or a mendicant, transforming someone into a nobleman and minister or turning someone into a poor and dejected person, kindling the spark of Faith in someone's heart or having the same snatched away from him, or turning a healthy person into a sick person and sick person into a healthy one. These attributes belong to Allah only and everybody, regardless of his status, is unable to do such things except Allah. Everyone is treated on an equal footing in terms of this inability.

The Prophets do not have the knowledge of the unseen:

The Prophets do not enjoy the distinction of having been awarded the keys to the unseen to the effect that they may have a cognizance of someone's innermost feelings or could make predictions about whether or not someone is going to be blessed with a child, whether one's business is going to yield profit or incur a loss, or whether someone is going to emerge victorious in a battlefield or face a defeat. As far as the above things are concerned, everybody is equally unaware about them regardless of his status. However, certain remarks which are made in reference to a certain context out of one's wisdom do sometimes come true. Similarly, these eminent people (i.e., the Prophets) make certain remarks in relation to a certain context using their own wisdom which sometimes prove to be correct and sometimes incorrect. But whatever information a Prophet is given through Divine Revelation is never incorrect, but the Revelation does not depend on a Prophet's own will.

The sayings of the Prophet {Peace be upon Him} regarding the knowledge of the unseen:

It has been narrated by Rubai' bint Muawwidh bin' Afra [2] : 

"The Prophet {Peace be upon Him} came to me while I was about to depart to my husband's house (after the completion of marriage ceremony) and sat next to me on my bed. Some of our young girls, to the accompaniment of the sound of a drumbeat, started narrating the saga of our martyrs during the battle of Badr. One of them even went to the extent of saying that our Prophet (who is amongst us) knows what is going to happen tomorrow. He (the Prophet {Peace be upon Him} said, "Stop what you are saying now and say what you have been saying before." (Al-Bukhari)

It means that on the occasion of Rubayi `Ansariya' s marriage ceremony, Prophet {Peace be upon Him} sat by her side. While singing frolickingly, the young girls made a remark saying that our Prophet knows what is going to happen tomorrow. The Prophet {Peace be upon Him} prohibited them from making such an utterance and asked them to refrain from it thenceforth. It thus becomes clearly known that a person no matter how pious and virtuous he is, we must not believe that he has the knowledge of the unseen. The poets, who keep eulogizing the Prophet {Peace be upon Him} by writing panegyric and laudatory poems extolling him to the skies and thereby justifying their uncalled for eloquence under the pretext of a mere exaggeration, is absolutely inc9rrect. So long as the Prophet {Peace be upon Him} did not even allow the young girls to recite verses in his praise, how could it be justifiable for an intellectual poet to verbalize or listen to such verses.

The saying of Aisha {May Allah have mercy on Her}: Aisha {May Allah have mercy on Her} stated:

"Whosoever ascribes the knowledge of five things to Allah's Prophet Muhammad {Peace be upon Him} which Allah has referred to in the verse saying: Allah has the knowledge of the Hour," (V.31:34), has attributed to him a monstrous calumny." (Al-Bukhari) 

It means that all the matters related to the unseen are covered under these five things that are stated at the end of Surah Luqman and mentioned earlier. Therefore, whoever says that the Prophet {Peace be upon Him} knew all the things belonging to the realms of the unknown, has indeed committed an immensely slanderous act. None has the knowledge of the Ghaib except Allah.

It has been reported by Umm Ala {May Allah have mercy on her} that the Prophet {Peace be upon Him} said: 

"Even though I am a Messenger of Allah, I can say swearingly by Him in the earnest, that I do not have a faintest idea as to what is going to happen to me or to you." (Al-Bukhari) 

It implies that the kind of treatment Allah is going to mete out to his slaves in this world, in their graves, or in the Hereafter is neither known by a Prophet, nor a sage. They neither know about themselves nor about the others. If someone happens to know about a certain person through Revelation that he is going to have a happy ending, such a piece of information thus acquired (through Revelation) is regarded to be no more than a brief and superficial knowledge. Acquiring any further knowledge is beyond their capacity.