Abu Dawud Book 1, Hadith Number 102.

Chapter : The utterence of bismillah in the beginning of ablution.

Narated By N/A : Explaining the tradition of the Prophet (PBUH) that ablution of a person who does not mention the name of Allah (in the beginning) is valid, Rabi’ah said: The tradition means that if a person performs ablution and takes a bath but does not have the intention to perform ablution for prayer and purify himself from sexual defilement, his ablution or bath is not valid.