Sahih Bukhari Volume 8, Book 77, Hadith Number 597.

Narated By Abu Huraira : Allah’s Apostle was asked about the offspring of the pagans. He said, “Allah knows what they would have done (were they to live).”

Narrated Abu Huraira: Allah’s Apostle said, “No child is born but has the Islamic Faith, but its parents turn it into a Jew or a Christian. It is as you help the animals give birth. Do you find among their offspring a mutilated one before you mutilate them yourself?” The people said, “O Allah’s Apostle! What do you think about those (of them) who die young?” The Prophet said, “Allah knows what they would have done (were they to live).”