(6) بَاب مَعْنَى كُلِّ مَوْلُودٍ يُولَدُ عَلَى الْفِطْرَةِ وَحُكْمِ مَوْتِ أَطْفَالِ الْكُفَّارِ وَأَطْفَالِ الْمُسْلِمِينَ
Abu Huraira reported that Allah's Messenger (ﷺ) was asked about the children of the polytheists, whereupon he said:
It is Allah Who knows best what they would be doing.
Reference: Sahih Muslim 2659 b
In-book reference: Book 46, Hadith 41
USC-MSA web (English) reference(deprecated numbering scheme): Book 33, Hadith 6430