Sahih Muslim Book 33, Hadith Number 6436.

Chapter : Everyone is born according to his true nature and the command pertaining to the demise of the children of the infidels and of the children of the Muslims.

‘Aisha, the mother of the believers, said that Allah’s Messenger (may peace be upon him) was called to lead the funeral prayer of a child of the Ansar. I said: Allah’s Messenger, there is happiness for this child who is a bird from the birds of Paradise for it committed no sin nor has he reached the age when one can commit sin. He said: ‘Aisha, per adventure, it may be otherwise, because God created for Paradise those who are fit for it while they were yet in their father’s loins and created for Hell those who are to go to Hell. He created them for Hell while they were yet in their father’s loins.