Zakaah on the mahr that is deposited in the bank
Question

                Is zakaah due on the mahr that has been kept in the bank since I got married and I do not want to buy anything with it? If that is the case, how should I pay zakaah on it?.
Praise be to Allah.If a person owns wealth 
    that reaches the nisaab (minimum threshold) and one full year has passed, he 
    must pay zakaah on it, whether this wealth is cash, gold or silver, from the 
    mahr (dowry) or anything else, whether he is saving it for a trip or to 
    build a house or any other purpose. 
The nisaab is the 
    equivalent of 85 grams of gold or 595 grams of silver. 
Based on that, if your mahr 
    that is kept in the bank is equivalent to the nisaab or more, then you must 
    pay zakaah on it every time one hijri year passes, so you must pay 
    one-quarter of one-tenth of it (2.5%). 
We must also point out that 
    it is not permissible to keep money in riba-based banks except in cases of 
    necessity or fear, to protect it, if there are no Islamic banks, so long as 
    there is no interest involved. 
And Allaah knows best.