What is the ruling on a husband’s insistence on buying household necessities with a credit card that is paid off with interest, while refusing to purchase them himself and not providing sufficient money, and is the wife sinful for accepting authorization to act on behalf of her husband in managing an interest-bearing bank deposit, knowing this, but without the deposit being in her name or her taking any of its interest?

Directly purchasing household necessities, such as food, drink, and other items, is determined by custom. If the custom is that the wife buys these things, then it is her responsibility, unless the husband volunteers and takes care of that expense for her. If the custom is that the husband buys them, then it is not permissible to compel the wife to buy them, unless she volunteers to do so.

If there is a concern about fitna (strife/temptation) arising from the wife going out to the markets, then she must be prevented, and the husband must take care of that for her.

It is not permissible to deal with credit cards that involve a usurious contract, as this constitutes cooperation in sin and aggression.

As for accepting authorization to manage one's money deposited in a bank, there is no harm in it if the management is of the principal amount only, without the interest. This is because the interest is not rightfully his, and it must be spent on general Muslim welfare or given to the poor and needy.