Making Vows to Others

Narrated by Ibn 'Umar, radhiAllaahu 'anhu: The Prophet, sallAllaahu 'alayhi wa sallam, forbade making vows, and said that, 

"It does not bring good. Indeed, it is only a means by which something is extracted from the miserly." 

[Agreed Upon]

Footnotes: A forbidden vow is like affirming that: 'if my sick person recovers, I will give away such and such amount as charity.' This means that he is not offering a charity purely for Allaah's sake but in fact intends to trade it in for a reward. Exactly a similar situation applies to a miserly person who does not undertake to perform a good thing except in return for a recompense. One must also bear in mind that making a vow or an offering does not affect a change in one's destiny. This is with regard to a vow that is made in the Name of Allaah. What about a vow that is made on someone's grave believing that 'the one who is lying in this grave will change my destiny or relieve my troubles or bring me some benefit'? This kind of vow is absolutely forbidden, and is a form of Shirk.

Bulugh al-Maram, p. 441