Is it permissible for the husband to send his wife's Zakat al-mal to his brother to pay off his debt, while the money remains with the brother for years due to a dispute over the amount of the debt, in hopes of reaching a settlement?

If the husband takes money from his wife with the intention of it being Zakat for the purpose of paying off his debt, her obligation is fulfilled, and the money enters his possession. It is permissible for the husband to delay repaying the debt until he reaches an agreement with the creditors. However, he must return any surplus to his wife, because he possesses the money with a restricted ownership, solely for the purpose of settling the debt. So, if a debtor receives money to pay off his debt, he is not permitted to spend it on anything else. But if he takes the money due to his poverty, he may dispose of it as he would with the rest of his own money.