Volume 8 · Book 78 · Hadith 684
Narrated 'Abdullah bin 'Umar: The Prophet forbade the making of vows and said, "It (a vow) does not prevent anything (that has to take place), but the property of a miser is spent (taken out) with it."
— Sahih Bukhari, Volume 8, Book 78: Oaths and Vows, Hadith #684