(6) بَاب مَعْنَى كُلِّ مَوْلُودٍ يُولَدُ عَلَى الْفِطْرَةِ وَحُكْمِ مَوْتِ أَطْفَالِ الْكُفَّارِ وَأَطْفَالِ الْمُسْلِمِينَ
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
No babe is born but upon Fitra. It is his parents who make him a Jew or a Christian or a Polytheist. A person said: Allah's Messenger, what is your opinion if they were to die before that (before reaching the age of adolescence when they can distinguish between right and wrong)? He said: It is Allah alone Who knows what they would be doing.
Reference: Sahih Muslim 2658 e
In-book reference: Book 46, Hadith 37
USC-MSA web (English) reference(deprecated numbering scheme): Book 33, Hadith 6426