What is the fate of those whom the message of Prophet Muhammad (peace be upon him) did not reach, and how will they be held accountable?

Whoever receives the message of Islam and does not believe in it will be resurrected on the Day of Judgment with the deniers. The proof for this is the Almighty's saying: "Say, 'What thing is greatest as a witness?' Say, 'Allah is witness between me and you. And this Qur'an has been revealed to me that I may warn you thereby and [warn] whoever it reaches.'" As for those whom the religion did not reach, at any time or place, they will be treated like the people of the Fatrah (an interval between two prophets). It cannot be definitively stated that there are people who have not heard the message of the Prophet, peace and blessings be upon him, but their existence may be presumed in isolated places such as the jungles of Africa and parts of Asia due to ignorance and isolation.