Abu Dawud Book 36, Hadith Number 4950.

Chapter : Not known.

Narated By ‘Aisha, Ummul Mu’minin : A woman came to the Apostle of Allah (PBUH) and said: Apostle of Allah! I have given birth to a boy, and call him Muhammad and AbulQasim as kunyah (surname), but I have been told that you disapproved of that. He replied: What is it which has made my name lawful and my kunyah unlawful, or what is it which has made my kunyah unlawful and my name lawful?