Ruling on paying the monetary value of a vow in a different currency
9-8-2015 | IslamWeb
Question:
I made a vow that I will donate ten Kuwaiti Dinars from my monthly salary to our brothers in Palestine, but right now I am spending the summer vacation in Egypt. Is it permissible to transfer the equivalent value of this sum of money in Egyptian pounds? Is it permissible to donate this money to another charity such as the National Cancer Institute, for example? Will it be obligatory on me to offer expiation as a result of this change (into a different currency) if it is permissible?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
If a Muslim makes a vow to do an act of obedience to Allaah, the Exalted, then he is obliged to deliver on it exactly as he had vowed. Allaah, the Exalted, described His pious slaves and what He prepared for them in Paradise and underlined their state in this worldly life. He says (what means): {Indeed, the righteous will drink from a cup [of wine] whose mixture is of Kafoor, a spring of which the [righteous] servants of Allaah will drink; they will make it gush forth in force [and abundance]. They [are those who] fulfill [their] vows and fear a Day whose evil will be widespread.} [Quran 76:5-7]
Fulfilling vows is one of the attributes of righteous and pious people. Therefore, you should pay this money to the Palestinians only as long as you had so specified in your vow. It is impermissible for you to donate it to any other institute or charity. However, it is permissible to pay this money to them in any other currency that is easier and more convenient for them, whether it is Egyptian pounds or any other currency, provided that you offer the exact sum of money that you specified in the vow. If you transferred the exact sum of money in Egyptian pounds to them without any decrease, then this is alright and it is not incumbent on you to offer any expiation because what is required is to fulfill your vow and then you would have done so.
Allaah Knows best.