Spending unlawful money on wedding does not affect validity of marriage
12-4-2017 | IslamWeb
Question:
Dear Brother/Sister, assalaamu alaykum. I would like to know whether the following statement can have an impact on the marriage: A husband was talking to his wife about interest money. He works within a family business where they take loans, and thus they are involved in interest money. He said to his wife that everything which is done with that money is haram, even their wedding, in the sense that the wedding is haram since all the costs were covered with money involving interest, just like the food that you buy with interest money is haram. Can this statement affect the wedding although at that the time the conversation was not about separation but rather about involvement in interest? Thank you.
Answer:
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad 
is His slave and Messenger.
The apparent meaning from the context is that the man does not mean to make his wife forbidden for him, but it means what you mentioned: that his marriage is haraam (unlawful) because the money spent on it was unlawful (according to his claim). However, if a person gets married with unlawful money, it does not affect the validity of his marriage.
It should be known that if he had earned that money from an interest-based loan, he is not considered as one consuming interest, as the actual interest is the interest which the bank takes.
Ibn Qudaamah 
said, “Any loan in which an extra amount (interest) is conditioned is forbidden without any difference of opinion. Ibn Al-Munthir said, ‘The scholars agreed in consensus that if the lender stipulates that the borrower pays a surplus amount or a gift and he lends on the basis that he takes an additional amount, then it is interest.’”
Hence, he – the man – helped in consuming interest, so he is sinful in this regard and must repent to Allah, but the money that he had taken is not unlawful.
If what he intended is other than what we understood from the question, then he is more aware of it.
Allah knows best.