Praise be to Allah.
It is part of the justice of Allah that He does not punish any people until He has first sent a warning to them and unless there is evidence against them. Allah does not treat anybody unfairly. Allah says (interpretation of the meaning): And We never punish until We have sent a Messenger (to give warning). [al-Israa 17:15].
In his tafseer (commentary) on this aayah, Ibn Katheer (may Allah have mercy on him) said: These words, And We never punish until We have sent a Messenger (to give warning) tell us of the justice of Allah, may He be exalted, and that He does not punish anyone until after He has established evidence against him by sending a Messenger to him. This is like the aayat (interpretation of the meaning): Every time a group is cast therein [into Hell], its keeper will ask, Did no warner come to you? They will say, Yes indeed; a warner did come to us, but we belied him and said: Allah never sent down anything (of revelation), you are only in great error. [al-Mulk 67:8] and: And those who disbelieved will be driven to Hell in groups, till, when they reach it, the gates thereof will be opened (suddenly like a prison at the arrival of its prisoners). And its keepers will say, Did not the Messengers come to you from yourselves, - reciting to you the Verses of your Lord, and warning you of the Meeting of this Day of yours? They will say: Yes, but the Word of torment has been justified against the disbelievers! [al-Zumar 39:71]
A person who has never heard of Islam or the Prophet (peace and blessings of Allah be upon him), and who has never heard the message in its correct and true form, will not be punished by Allah if he dies in a state of kufr (disbelief). If it were asked what his fate will be, the answer will be that Allah will test him on the Day of Resurrection: if he obeys, he will enter Paradise and if he disobeys he will enter Hell. The evidence (daleel) for this is the hadeeth of al-Aswad ibn Saree, who reported that the Prophet of Allah (peace and blessings of Allah be upon him) said: There are four (who will protest) to Allah on the Day of Resurrection: the deaf man who never heard anything, the insane man, the very old man, and the man who died during the fatrah (the interval between the time of Eesaa (Jesus, upon whom be peace) and the time of Muhammad (peace and blessings of Allah be upon him)). The deaf man will say, O Lord, Islam came but I never heard anything. The insane man will say, O Lord, Islam came but the children ran after me and threw stones at me. The very old man will say, O Lord, Islam came but I did not understand anything. The man who died during the fatrah will say, O Lord, no Messenger from You came to me. He will accept their promises of obedience, then word will be sent to them to enter the Fire. By the One in Whose hand is the soul of Muhammad, if they enter it, it will be cool and safe for them.
According to another report, he said: Whoever enters it, it will be cool and safe for him, and whoever does not enter it will be dragged to it.
(The hadeeth was reported by Imaam Ahmad and Ibn Hibbaan, and deemed saheeh by al-Albaani, Saheeh al-Jaami, 881).
Everyone who hears the message of Islam in a sound and correct form (and rejects it), will have evidence against him. Whoever dies without having heard the message, or having heard it in a distorted form, then his case is in the hands of Allah. Allah knows best about His creation, and He will never treat anyone unfairly. And Allah is All-Seer of His slaves.