Is the husband sinful who failed to pay the installments for the car registered in his wife's name, by agreement between them, which led to her being legally pursued and having to borrow to pay the debt, and is the borrowed amount his responsibility, and what is the ruling of Islamic law on his action?

The car either belongs to the husband or the wife:

- If it belongs to the husband, he is sinful if he does not pay the installments. He is obligated to pay them or compensate his wife for their cost.

- If it belongs to the wife: If his commitment to pay the installments was voluntary, then fulfilling it is recommended (mustahabb) but not obligatory according to the majority of scholars. Not fulfilling it is not sinful, but it is disliked (makrooh tanzeehan). However, if his commitment was in return for expenses the wife paid that were not her obligation, then she has the right to reclaim those expenses from him if he does not fulfill his promise.