People who have not heard of Islam

Question: Suppose that a person lives in the mountains, in the desert, in a cave, in a forest, or on an uninhabited island and he/she has not heard of any religions or prophets. If such a person cogitates and infers the existence of Allah through the use of mind or if he/she cannot realize His existence in his/her lifetime, what will his/her fate be in the Hereafter?
Those people who live in any of the abovementioned places and have not heard of any religions will not enter Paradise as they do not have faith (iman). They will not enter Hell because they have neither heard of the existence of Allah, Paradise and Hell nor rejected them. After rising from death and being questioned about their deeds, they will be non-existent in common with all animals. (Maktubat-i Rabbani, Faraid al-Fawaid)

Those who live in the mountains or in the desert and have not heard of prophets is called shaahiq al-jabal. Such people are excusable; they are not commanded to believe in prophets. (Ithbat-un-Nubuwwa) 

A person who never heard of the Prophet but thought to himself/herself “Allah exists and is One” and believed in this fact and died having only this faith, will go to Paradise, too. (Islam and Christianity)

The scholars from the city of Bukhara said, “An injunction is not done before the appearing of a prophet and his teaching the religion.” Imam-i Ash’ari said the same, and this is the preferred statement. Those very scholars said that the meaning of the statement “One who is wise enough cannot be exempted from [the liability of] knowing of the existence of Allahu ta’ala inasmuch as one sees the sky, the earth and oneself” conveys the connotation that “One will not be exempted from it after learning the fact from prophets.” (Radd-ul-Mukhtar)

Hadrat Imam-i Rabbani states:
There were scholars who said that one had to discern the existence and oneness of Allahu ta’ala through one’s mind. However, though Allahu ta’ala has created the mind so that it will distinguish right from wrong, it cannot find the right path by itself unless the mind is informed of that way. In the Hereafter, those who have not heard of prophets will suffer as much torment as their crimes require at the place of judgement. After everyone is given their rights, such people will be annihilated like all animals. (First Volume, Letter 259)

(We do not torment without first having sent a messenger[without communicating the religion].) [Al-Isra’ 15]

Will those people who have not ever heard of Islam enter Hell?
One of the sons of Hadrat Imam-i Rabbani asked his father the following question:

“If those who grew up in mountains without having heard any religions and worship idols will not remain in Hell eternally, they ought to enter Paradise. Yet this is impossible, because Paradise is prohibited for polytheists. The next world does not contain a place other than Paradise and Hell. Those who stay at A’raf will go to Paradise after a while. The place to remain eternally is either Paradise or Hell. Then in which one will those people stay?”

Hadrat Imam-i Rabbani answered:

“My dear son! As a solution to this problem, the statement, “Our Master the Prophet will invite them to Islam on the Day of Resurrection. Those who accept it will be put in Paradise, and those who refuse it will be sent to Hell,” does not sound tenable to this faqir[Hadrat Imam-i Rabbani means himself] because the next world is the place of rewards and reckoning. It is not a place of commandments or deeds; why should the Prophet be sent there on a mission, then! After a long time, Allahu ta’ala pitied me, and blessed me with a solution for this matter. I was informed that those polytheists will not remain either in Paradise or in Hell, but after being resurrected in the next world, they will be called to account and will suffer as much torment as their crimes require at the place of judgement. After everyone is given his/her rights, they will be annihilated like all animals. With the human mind so susceptible to confusion and error even in worldly affairs, it would be very offensive, according to this faqîr, to say that our Owner, whose goodness and mercy are boundless, will burn them eternally in the fire without informing them through His prophets only because they could not find out by using their minds. As it is out of place to say that such people will remain eternally in Paradise, so it is out of place to say that they will suffer eternal torment. Then, the true answer is the one that has been revealed to us. That is, after their accounts are settled on the Day of Judgement, they will be annihilated. (Vol. 1, Letter 259)