Abu Dawud Book 15, Hadith Number 3307.
Chapter : Not known.
Narated By Thabit ibn ad-Dahhak : In the time of the Prophet (PBUH) a man took a vow to slaughter a camel at Buwanah. So he came to the Prophet (PBUH) and said: I have taken a vow to sacrifice a camel at Buwanah.
The Prophet (PBUH) asked: Did the place contain any idol worshipped in pre-Islamic times?
They (the people) said: No.
He asked: Was any pre-Islamic festival observed there?
They replied: No.
The Prophet (PBUH) said: Fulfil your vow, for a vow to do an act of disobedience to Allah must not be fulfilled, neither must one do something over which a human being has no control.