Question:
Ahlul-Fatra (those people who lived during the break in the series of Messengers) were Mushrikūn (polytheists) kuffār (disbelievers). However, there is a party of the People of Knowledge who say, “Indeed Ahlul-Fatra will not be punished up until the divine proof has been established upon them.” So based on this statement, the following hadīth poses as a problem: “Indeed my father and your father are in the Fire.” [Muslim, hadith no.247]
That which is well known is that the father of the Messenger – صلى الله عليه وسلم – was before the sending (of the Prophet). So what is the principle rule in knowing who Ahlul-Fatra were and who the Mushrikūn were before the sending of the Messenger – صلى الله عليه وسلم –?

Answer:
Ahlul-Fatra are those who had no Prophet sent to them. Allāh, the Most-High, said,

“O People of the Scripture (Jews and Christians)! Now has come to you Our Messenger (Muhammad – صلى الله عليه وسلم –) making things clear to you, after a break in (the series of) Messengers, lest you say, “There came to us no bringer of glad tidings and no warner.”[Al-Māidah:19].

This is that period of time between ‘īsā (Jesus) and Muhammad – عليهما الصلاة والسلام – this is a period (of a break in the series of Messengers). Whoever died in this period of time, whilst there didn’t reach him anything from the (divine) Message, the message of Mūsā or ‘īsā, this person although he may have been upon shirk (polytheism), Allāh will raise him on the Day of Resurrection, examine and test him. This applies to the one who died in this period of time, the mentally disabled, the deaf person, the child, the old senile person who lacks understanding. This person will say, “No warner came to me in this period of time and had he come to me, I would have believed.” The mentally disadvantaged would say, “I was disadvantaged mentally, the children would push me into the side of the pathways.” Another would say, “He (the Messenger) came to me, yet I was feeble-minded and couldn’t hear.”
So Allāh will send to them a Messenger from the Angels or other than them, who will say to them, “enter the Fire!” So whoever from them is prepared to enter the Fire, will be considered as an obedient believer. And whoever rejects and refuses, will be considered a disbeliever who shall enter the Fire, because this person, if a warner came to him and established upon him the proof, he would contest and oppose him like the rest of the Mushrikīn. So this person would enter the Fire due to his disbelief.

It is possible that a person is from this period of time (fatra) yet the evidence reached him from the remnants of the religion of Ibrāhīm, Mūsā or ‘īsā. So this person, the proof has been established with him. Hence, the Messenger – صلى الله عليه وسلم – mentioned concerning some of the Mushrikīn – they are in the Fire, because the proof had reached them yet they refused to enter into the true religion – the religion of Islam.

Before the sending of Muhammad there remained something from the da’wah of Ibrāhīm – عليه السلام -. So to whoever it became apparent concerning that which the Arab were upon was Shirk, like with Waraqah ibn Nawfal and Zayd ibn ‘Amr ibn Nufayl and other than them, if he was to remain with his people with that which they were upon, this person would be from the People of the Fire. However, if he was to shun this Shirk and abandon it as did Waraqah and his companions, then these – if Allāh wills – are from the People of Salvation.

The proof cannot be established until a person hears the evidence and understands it. So when you come and read to an Indian person for example, a non-Arab who doesn’t know Arabic and you read the Qur’ān to him, (can we say) the evidence has been established upon him? Another person is English! Another American! Is this the way the da’wah of the Messenger was?!

Therefore it is necessary to establish the clear proof. The Messenger – صلى الله عليه وسلم – used to explain and make clear. So when he used to write to Caesar and Chosroes, there was for them translators who would translate for them so they understood. So once they understand, the proof is then considered as being established and (if they refuse and) want to fight us, we fight them, and if we’re not able, Allāh is in charge of their affair and the proof has been established upon them.

Fatāwā Faḍeelatis-Shaykh Rabī’ Al-Madkhalī, Majmū’ Kutub Wa Rasāil Wa Fatāwā Ash-Shaykh Al-‘Allāmah Rabī’ bin Hādī Al-Madkhalī  – Volume 14, page 318 – 320, fatwā no. 48 & 104 (combined together and abridged).
Translated by Abū Humayd Sālim.