Reference: Fataawa Islaamiyyah – Volume 1, Page 108
Question: What is the final destination of those who lived during the period of the messenger of Allaah, ‘Eesaa (Jesus) (‘alayhis-salaam), and before the beginning of the mission of our messenger, Muhammad (sal-Allaahu ‘alayhi wa sallam). Are they considered to belong to Ahlul-Fitrah?
Response: The correct statement is that Ahlul-Fitrah are divided into two categories: The first category is the one before whom the evidence is established, and he recognised the truth, yet followed what he found his forefathers following. In this case, there is no excuse for him and he is among the inhabitants of the Fire; As for the one before whom the evidence has not been established, his matter is for Allaah, the Almighty and Majestic, to decide. And we do not know his final destination. This is because we do not know of a Sharee’ah text (ruling) for that case. But in the case of one about whom it is confirmed that he will be in the Fire based upon authentic evidence, then he is in the Fire.