Abu Dawud Book 15, Hadith Number 3307.

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.