Is a son's marriage considered invalid if he marries using money he knows comes from a haram source from the bank, while his mother, who owns the money, was unaware of its impermissibility?

The impermissibility of usurious gains is not intrinsic to the gains themselves but to the financial liability of their holder. Therefore, a mother marrying off her son using usurious gains does not affect the validity of the marriage. Whoever acquires illicit wealth must dispose of it by spending it on charitable causes. As for the marriage itself, it remains valid. However, the amount of the dowry paid, if it came from illicit earnings, must be disposed of, accompanied by sincere repentance. If the mother acquired the usurious gains while ignorant of their impermissibility and then repented, she is not required to return what she previously spent.