What did Prophet Muhammad (saw) determine was the rightful owner of the boy based on the dispute between Sa`d bin Abi Waqqas and 'Abu bin Zam`a?
 Narrated `Aisha:                     Sa`d bin Abi Waqqas and 'Abu bin Zam`a had a dispute over a boy. Sa`d said, "O Allah's Apostle! This (boy) is the son of my brother, `Utba bin Abi Waqqas who told me to be his custodian as he was his son. Please notice to whom he bears affinity." And 'Abu bin Zam`a said, "This is my brother, O Allah's Apostle! He was born on my father's bed by his slave girl." Then the Prophet looked at the boy and noticed evident resemblance between him and `Utba, so he said, "He (the toy) is for you, O 'Abu bin Zam`a, for the boy is for the owner of the bed, and the stone is for the adulterer. Screen yourself before the boy, O Sauda bint Zam`a." `Aisha added: Since then he had never seen Sauda.