Hadith 6608
Narrated Ibn `Umar: The Prophet forbade vowing and said, "In fact, vowing does not prevent anything, but it makes a miser to spend his property."
Hadith 6609
Narrated Abu Huraira: The Prophet said (that Allah said), "Vowing does not bring to the son of Adam anything I have not already written in his fate, but vowing is imposed on him by way of fore ordainment. Through vowing I make a miser spend of his wealth."