My question is about the interest my father receives from a saving account in a bank. I know that interest is Haram and I have informed him of the punishment which Allah will give in Qiyamah to the person who deals in interest. But he fails to understand. I'm not sure whether my prayers are valid; according to Hadith a person who deals in interest his prayers are of no use. What should I do to convince my father to stop taking interest?

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.

Know that Riba (usury/interest) given by banks is forbidden since the prohibition of Riba is among the known facts of the Sharee’ah.

Allah Says (what means): {O you who have believed, fear Allah and give up what remains [due to you] of interest, if you should be believers.} [Quran 2:278]

Jaabir narrated that the Prophet said “Allah has cursed the one who consumes Riba (i.e. usury or interest), the one who gives it to others, the one who records it and the one who witnesses it (its transaction).” He added: “All of them are equal in sin.” [Muslim]

A Muslim has to submit himself to the commands of the Sharee’ah and should not go beyond the limits set by it.  You did well by advising your father to give up dealing with usury-taking banks and to get rid of Riba by spending it in the welfare of the Muslims. By doing so, you have fulfilled your duty and your father will bear the sin. You are no longer responsible for that sin; Allah Says (what means): {…and no bearer of burdens shall bear the burden of another….} [Quran 6:164]

If you are enquiring about the rulings of using your father’s money which is from Riba, the answer is that using ill-gotten money which is not mixed with any lawful money is not permitted. However, if the money is mixed between what is lawful and what is forbidden, then one may use it, though it is not desirable since it may lead to dealing with forbidden earnings.

As for the person who uses his parents' ill-gotten earnings, then the ruling depends on his situation. If the person cannot spend on himself due to his young age, or due to being busy in studies, then he is considered as a compelled person; thus, he may use such earnings while detesting it in his heart till he becomes able to earn for himself.

As for the Hadeeth that the prayers of the one who deals with Riba are not accepted, then we did not find any Hadeeth with such wording.  But there is a Hadeeth in Saheeh Muslim that Allah does not accept the Du’a (supplication) of the one whose food or drink, is from what is forbidden; Riba is, in fact, is among the major forbidden acts. The Hadeeth reads: “…Then, he, sallallahu ‘alayhi wa sallam, mentioned a man who travels a long distance with his hair disheveled and covered in dust, then he raises his hand towards the sky (and supplicates Allah), 'O Lord, O Lord,' while his food is unlawful, his drink is unlawful, and his clothes are unlawful and his nourishment is unlawful. How then would his supplication be accepted?" [Muslim]

Imam an-Nawawi said about the interpretation of this Hadeeth:

“The meaning of this Hadeeth – Allah Knows best –is that the person covers a long distance in his travel such as travelling for Hajj, or for keeping kin relations, or to perform a desirable visit, but how could the supplications of the one whose situation is as in the above Hadeeth be answered.’

However, one should know that there is a difference between the acceptance of the prayers and being free from the obligation. The prayers of the person who consumes what is forbidden suffice him, i.e. he is not ordered to repeat them, but it does not necessarily mean that they are accepted.  However, Allah may accept them due to His great favour on His slaves.

Al-Qurtubi said: “The wording of the Hadeeth ‘How then would his supplication be accepted?’, means that he is not qualified to be responded to even though Allah may accept his supplication as a favour upon him.”

Allah knows best.