From Sahih Bukhari (Hadith 6600):
Narrated Abu Huraira:Allah's Messenger (ﷺ) 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 Messenger (ﷺ)! What do you think about those (of them) who die young?" The Prophet (ﷺ) said, "Allah knows what they would have done (were they to live)
Reference: Bukhari 6600