A nikaah took place in which half of the mehar was paid and half was decided to be paid later.
However after a year the wife said to the husband that she forgives the remaining portion of mehar and she doesn't want it. After 3 years divorce took place between this couple and the husband gave her talaaq.
Now after 6 months the wife is asking for the rest of her mehar, insistently saying that she wants it as she needs it. The husband, however says this mehar is not due on him now because she had already forgiven him the remaining portion of mehar.
How should this matter be resolved?