Sahih Muslim
The Book of Vows (Kitab Al-Nadhr)
Book Number: 014 / Hadith Number: 4021
Ibn Umar reported that Allah's Apostle (may peace be upon him) forbade (people) taking vows, and said: It does not (necessarily) bring good (in the form of substantial, and tangible results), but it is the meant whereby something is extracted from the miserly persons.