Is it obligatory to fulfill a vow to buy a suit for a deceased person, knowing that his son, who is addicted to alcohol, might use its price for drinking?

The contingent vow is disliked, but it must be fulfilled if it is an act of obedience (qurbah) and the condition upon which it was made is met. If the vow is a charity, it is obligatory to fulfill it for the heirs of the intended recipient, because it has become their property, and the vow is not invalidated by his death. However, if the vow is a gift, it is not obligatory to fulfill it because it is a permissible vow, and a vow is only binding if it is an act of obedience, and its maker has the choice between fulfilling it or atoning for it with an expiation for an oath.