Her husband gave her a mahr of a car that he bought by means of riba; now he wants to take it back so he can buy another car by permissible means
Question

                For my mahr, I asked for a family car. My husband obtained this 5 months into our marriage. The car we got has interest on the payments, so now he wants to take the car back and get a different one with halal payments. Is he allowed to take back my mahr without my permission?
Praise be to Allah.
      So long as your husband gave you this car as a mahr and you 
      took possession of it, it has become your property, so it is not 
      permissible for him to take it back from you against your wishes. Allah, 
      may He be glorified, has forbidden husbands to take anything of their 
      wives’ mahrs except that which the wives give willingly. Allah, may He be 
      exalted, says (interpretation of the meaning):

    “And give to the women (whom you 
    marry) their Mahr (obligatory bridal money given by the husband to his wife 
    at the time of marriage) with a good heart, but if they, of their own good 
    pleasure, remit any part of it to you, take it, and enjoy it without fear of 
    any harm (as Allah has made it lawful)”

    [an-Nisa’ 4:4]

    “But if you intend to replace a 
    wife by another and you have given one of them a Cantar (of gold i.e. a 
    great amount) as Mahr, take not the least bit of it back; would you take it 
    wrongfully without a right and (with) a manifest sin?”

    [an-Nisa’ 4:20].

    But… If your husband wants to get out of this riba-based 
    transaction by selling this car and paying off the remaining riba 
    instalments, then buying another car for you by permissible means, then our 
    advice to you is to help him to do that, and seek reward for that from 
    Allah, may He be glorified. Let your intention be to help him in repenting 
    and to get out of this prohibited transaction, for Allah has decreed 
    kindness in all things, and the most deserving of people of your kindness is 
    your husband.

     And Allah knows best.