They are from Ahlul-Fitrah

Question:

The Revealed Books prior to the Qur'an were altered, then came later generations and they continued to follow the path of these Books, without knowing that they had been altered, so what will be the position of these generations before Allah, the Most High on the Day of Resurrection?

Answer:

There were people who deliberately falsified (their Scriptures) and removed certain punishments and changed some of them. These people carry two sins -altering (the Scriptures), and misguiding those who came after them. There are others who acted upon them, even though they know that they have been altered; and they recite them (as they are), even though they know what the correct reading should be. They carry the sin of deliberately acting upon what has been corrupted. There are still other people who are ignorant and unlettered, who follow these laws and act upon them, without searching for what is correct and original. They carry some sin, but if they are unlettered and unable to ascertain the truth, then their sin is carried by those who misled them. And if they are unable to ascertain the truth and find none to ask, then they will be judged as Ahlul-Fitrah, who will be tested in the Hereafter and it will become clear from Allah's Knowledge who is a believer, and Allah knows best.

Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 1 Pages 203-204