Some people make vows such as: If Allaah cures me, I will give such and such in charity. Such vows do not change destiny. What is to happen will happen. They are just a means for the miser to give in charity.

In come places of the world this is also known as a mannat

'Abdullah bin Umar reported:

Allah's Messenger (sallallaahu alayhi wa sallam) singled out one day forbidding us to take vows and said: It would not avert anything; it is by which something is extracted from the miserly person.

[Sahiih Muslim 1639]

It was narrated that 'Abdullah bin 'Umar said:

"The Messenger of Allah forbade vows and said: 'They do not change anything; they are just a means of taking wealth from the miserly.'"

[Sunan al-Nasaa'i 3802]