Is the father obligated to fulfill his promise to pay a sum of money to his son's wife in exchange for her finding him a wife, given his financial inability and the son's refusal to pay on behalf of his father, and are the children obligated to pay the sum on behalf of their father if he is unable to do so?

If a father commissions a woman to find a wife for him in exchange for a sum of money, this is a permissible brokerage akin to a jua'la (commission/reward-based contract), and the woman is entitled to the agreed-upon amount after fulfilling the request. If the father is unable to pay the full amount, the remainder is a debt owed by him, and it is recommended for the children to pay it on his behalf. However, if it was merely a promise, fulfilling it is considered mandub (recommended) by the majority of scholars, while some scholars have deemed it obligatory, because breaking a promise is considered a branch of practical hypocrisy.