From Sahih Bukhari (Hadith 1385):
Narrated Abu Huraira:The Prophet (ﷺ) said, "Every child is born with a true faith of Islam (i.e. to worship none but Allah Alone) and his parents convert him to Judaism or Christianity or Magianism, as an animal delivers a perfect baby animal. Do you find it mutilated?
Reference: Bukhari 1385