Narrated Abu Huraira:

Allah's Messenger (ﷺ) said, "No child is born except on Al-Fitra (Islam) and then his parents make him Jewish, Christian or Magian, as an animal produces a perfect young animal: do you see any part of its body amputated?" Then he rec 'The religion of pure Islamic Faith (Hanifa),(i.e. to worship none but Allah), The pure Allah's Islamic nature with which He (Allah) has created mankind. Let There be no change in Allah's religion (i.e. to join none in Allah's worship). That is the straight religion; but most of men know not..." (30.30)

حَدَّثَنَا عَبْدَانُ، أَخْبَرَنَا عَبْدُ اللَّهِ، أَخْبَرَنَا يُونُسُ، عَنِ الزُّهْرِيِّ، قَالَ أَخْبَرَنِي أَبُو سَلَمَةَ بْنُ عَبْدِ الرَّحْمَنِ، أَنَّ أَبَا هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ مَا مِنْ مَوْلُودٍ إِلاَّ يُولَدُ عَلَى الْفِطْرَةِ، فَأَبَوَاهُ يُهَوِّدَانِهِ أَوْ يُنَصِّرَانِهِ أَوْ يُمَجِّسَانِهِ، كَمَا تُنْتَجُ الْبَهِيمَةُ بَهِيمَةً جَمْعَاءَ، هَلْ تُحِسُّونَ فِيهَا مِنْ جَدْعَاءَ ‏"‏ ثُمَّ يَقُولُ ‏{‏فِطْرَةَ اللَّهِ الَّتِي فَطَرَ النَّاسَ عَلَيْهَا لاَ تَبْدِيلَ لِخَلْقِ اللَّهِ ذَلِكَ الدِّينُ الْقَيِّمُ‏}
USC-MSA web (English) reference : Vol. 6, Book 60, Hadith 298
Arabic reference : Book 65, Hadith 4775