Is it permissible for the husband to take his wife's dowry (car), which he purchased unlawfully without her permission, in order to return it and buy another car through lawful means?

If the wife takes possession of the car as a dowry (mahr), it becomes her property, and the husband is not permitted to reclaim it unless she allows it. This is based on the Almighty's saying: (And give women their dowries with a good heart; but if they, of their own good pleasure, remit any part of it to you, take it and enjoy it with good cheer and satisfaction) and (But if you intend to replace a wife with another and you have given one of them a qintar [a great amount of wealth], do not take anything back from it. Would you take it in falsehood and manifest sin?).

However, if the husband wishes to sell it to pay off usurious installments and purchase another car through permissible means, the wife is advised to help him with that, seeking reward from Allah, with the intention of assisting him in repentance and exiting a prohibited transaction.