The Messenger of Allah ﷺ said, "Every child is born upon the natural disposition, then his parents make him a Jew, a Christian, or a Magian, just as an animal gives birth to a whole offspring. Do you find any of them mutilated?"Then he would say, "Recite if you wish, 'The natural disposition of Allah upon which He has created mankind. There is no altering Allah's creation' [Rum 30:30]."
حدثنا عبد الرزاق حدثنا معمر عن الزهري عن ابن المسيب
قال رسول الله ﷺ كل مولود يولد على الفطرة فأبواه يهودانه وينصرانه ويمجسانه كما تنتج البهيمة هل تحسون فيها من جدعاء ثم يقول واقرءوا إن شئتم {فطرة الله التي فطر الناس عليها لا تبديل لخلق الله}
Its isnad is sahih. Muslim also related it, 2:301, from Ubayd bin Humayd, from Abdul-Razzaq, with this same isnad. He did not mention its wording, referring instead to what he had already given from the narration of Zubaydi from Zuhri. Ibn Hibban related it in his Sahih, number 130 in our edition, by way of Ishaq bin Rahawayh, from Abdul-Razzaq. It has already passed in a slightly shorter form as 7181, from Abdul-Ala, from Maamar. Its meaning has also already passed in the narration of Abu Salih, from Abu Hurairah, 7436, 7437, 7438, and we have documented it through many routes in the hadith of Ibn Hibban, number 128.