كتاب القدر
46
The Book of Destiny
(6)
Chapter: The Meaning Of "Every Child Is Born In A State Of Fitrah" And The Ruling On The Dead Children Of The Disbelievers And Of The Muslims.
(6)
بَاب مَعْنَى كُلِّ مَوْلُودٍ يُولَدُ عَلَى الْفِطْرَةِ وَحُكْمِ مَوْتِ أَطْفَالِ الْكُفَّارِ وَأَطْفَالِ الْمُسْلِمِينَ
Sahih Muslim 2659 a

Abu Huraira reported Allah's Messenger (ﷺ) as saying:

The mother of every person gives him birth according to his true nature. It is subsequently his parents who make him a Jew or a Christian or a Magian. Had his parents been Muslim he would have also remained a Muslim. Every person to whom his mother gives birth (has two aspects of his life) ; when his mother gives birth Satan strikes him but it was not the case with Mary and her son (Jesus Christ).
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، - يَعْنِي الدَّرَاوَرْدِيَّ - عَنِ الْعَلاَءِ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ كُلُّ إِنْسَانٍ تَلِدُهُ أُمُّهُ عَلَى الْفِطْرَةِ وَأَبَوَاهُ بَعْدُ يُهَوِّدَانِهِ وَيُنَصِّرَانِهِ وَيُمَجِّسَانِهِ فَإِنْ كَانَا مُسْلِمَيْنِ فَمُسْلِمٌ كُلُّ إِنْسَانٍ تَلِدُهُ أُمُّهُ يَلْكُزُهُ الشَّيْطَانُ فِي حِضْنَيْهِ إِلاَّ مَرْيَمَ وَابْنَهَا ‏"‏ ‏.‏
Reference : Sahih Muslim 2659 a
In-book reference : Book 46, Hadith 40
USC-MSA web (English) reference : Book 33, Hadith 6429
  (deprecated numbering scheme)