Hadith on Fitrah:

Narrated Abu Huraira (رضي الله عنه): The Messenger of Allāh (صلى الله عليه وسلم) said, “No one is born except they are upon Al-Fitrāh (instinct). His parents turn him into a Jew or Christian or Magian, just as animals produce their young with perfect limbs. Do you see anything defective?” Then Abu Hurairah, recite the verse if you wish, “So direct your face toward the religion, inclining to truth. [Adhere to] the fitrah of Allāh upon which He has created [all] people. No change should there be in the creation of Allāh. That is the correct religion, but most of the people do not know.” [Surah Ar-Rūm 30:30]

[Sahih Muslim, Book 033, Number 6423]

عَنْ أَبِي هُرَيْرَةَ، أَنَّهُ كَانَ يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم‏ مَا مِنْ مَوْلُودٍ إِلاَّ يُولَدُ عَلَى الْفِطْرَةِ فَأَبَوَاهُ يُهَوِّدَانِهِ وَيُنَصِّرَانِهِ وَيُمَجِّسَانِهِ كَمَا تُنْتَجُ الْبَهِيمَةُ بَهِيمَةً جَمْعَاءَ هَلْ تُحِسُّونَ فِيهَا مِنْ جَدْعَاءَ‏ ‏.‏ ثُمَّ يَقُولُ أَبُو هُرَيْرَةَ وَاقْرَءُوا إِنْ شِئْتُمْ‏ فِطْرَةَ اللَّهِ الَّتِي فَطَرَ النَّاسَ عَلَيْهَا لاَ تَبْدِيلَ لِخَلْقِ اللَّهِ‏ الآيَةَ