Is it permissible for a husband to pay off his father-in-law's debts from his Zakat money, knowing that his father-in-law is well-off and owns land that he refuses to sell a portion of to pay off his debt?

If a father incurs debts for his own benefit, and he possesses land in excess of his basic needs that enables him to pay off his debts, then he is not considered among the debtors (gharimin) to whom Zakat (definition) may be given. He is obligated to sell enough of the land to settle his debt, based on the Prophet's (peace be upon him) saying: "The procrastination of a rich person (in paying debts) is an injustice," and his saying: "The delay of one who has means (to pay debts) makes his honor and punishment permissible."