He promised his mother to give her money that she could put towards building a mosque, then she died
Question

                My mother asked me for some money that she could put towards a mosque that was being built in our village, but at that time I did not have any money that was surplus to my needs with which I could fulfil her request. So I promised her that in the future I would give her money if Allaah willed. Then I travelled outside of my country to seek halaal provision. During that period, Allaah decreed that my mother fell sick and she died as a result. Does that promise that I made to her remain as a debt that I owe, and do I have to give what I promised her to that particular mosque, or is it permissible to give it to another mosque that needs money, or is that promise no longer a debt that I owe and am I thus pardoned from it?.
Praise be to Allah.
    Yes, you must certainly fulfil your promise and give that 
    money to the mosque that your mother wanted to give it to, as that you 
    promised to do. It is part of honouring her and treating her kindly to 
    fulfil this promise, in the hope that Allaah, may He be glorified and 
    exalted, will accept its and benefit her thereby. This is part of honouring 
    her and treating her kindly. If the mosque that your mother wanted to 
    support has no need of it and its expenses are covered, then you may give it 
    to any other mosque, but as we have mentioned, you should not neglect this 
    promise and fail to give this money, rather you should and most certainly must fulfil this promise, as a way of honouring your mother. And Allaah knows best. End quote.