The Messenger of Allah ﷺ said, "Every child is born upon the natural disposition, and it is his parents who make him a Jew, a Christian, or a polytheist."A man asked, "Messenger of Allah, what if he dies before that?"He replied, "Allah knows best what they would have done."
قال رسول الله ﷺ: ما من مولود إلا جرير، عن يولد على الفطرة، فأبواه يهودانه وينصرانه ويشر كانه. فقال رجل: يا رسول الله، أرأيت لو مات قبل ذلك؟ قال: الله أعلم بما كانوا عاملين.
Muslim narrated it in al-Qadar (2658:23) from Zuhayr bin Harb, who reported to us from Amash, from Abu Salih, from Abu Hurairah, and mentioned it. He also narrated it through another route from Ibn Numayr and Abu Muawiya, both from Amash with this same chain of transmission. However, in Ibn Numayr's version it reads, "There is no newborn born except that he is upon the natural disposition." And in Abu Muawiya's version it reads, "except upon this natural disposition, until his tongue expresses it clearly for him." And in another narration from him, "until his tongue speaks for him."