I am the cause of my father being unable to get interest of around 30,000 taka every year. As revenge, he ordered me to give this money from my own pocket every year. I thought that it was obligatory to obey him in this regard, and so I told him (without saying 'I promise') that I would do so. Does this mean that it has become obligatory upon me to give him this money every year? [Please note that he is quite rich and solvent.]

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

Interest is one of the grave major sins, and it is one of the reasons that cause the Wrath of Allah. It is not permissible to help in it, as it is a clear sin. Allah says (what means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty...} [Quran 5:2]

Indeed, you did well by preventing your father from dealing with interest.

Your father does not have the right to oblige you to pay all this money to him, and you are not obliged to give it to him. The obedience to the father is obligatory only in what is permissible, and it is not at all permissible for him to take money from his son in a manner that harms him.

To learn about the limits of obedience to parents, please refer to fatwas 84942 and 87211.

Regarding the saying of the Prophet “You and your wealth belong to your father,” [Ibn Maajah], Al-Khattaabi said, “He said to him, 'You and your wealth belong to your father,' meaning if he is in need of your money, he takes according to his need, and if you have no money and you can earn money by working, then you are obliged to work and spend on him. But to say that the meaning is that the son's money is lawful to his father and that he may abuse it and spend it in an extravagant and wasteful manner, then I do not know of any scholar who is of this opinion.”

For more benefit on interest, please refer to fatwa 89942.

Finally, we advise you to be wise in dealing with your father in order to avoid his anger or any dissension with him.

Allah knows best.