Musnad Ahmad 30:1442

'Affan narrated to us, Hammad ibn Salamah narrated to us, from Qays, from Tawus, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no newborn except that he is born upon the *fitrah* (natural disposition), until his parents are the ones who make him a Jew or make him a Christian, just as you produce your livestock—do you see any among them that is born mutilated until you yourselves mutilate them?" A man said: "Then where are they?" He said: "Allah knows best what they would have been doing." Qays said: "I do not consider that man to be anything other than a Qadari."