Sheikh Muhammad Iqbal Nadvi, Imam of Calgary Mosque, Alberta, Canada, and Former Professor at King Saud University, Riyad, Saudi Arabia, states:
1. If you are not sure from the beginning that a person’s money is halal (lawful) or haram (unlawful) wholeheartedly, then you are not supposed to dig deep in the matter in order to get accurate information for something that you don’t need to. So, if someone gives you a gift, and you are not sure whether his money is all halal or haram, then you are allowed to accept his gift without questioning.
2. If someone has money that is mixed from haram and halal sources, but the halal source is more, then the money of this person is halal in general, but he has shubha (doubt) in his money. In this case, we are still allowed to accept the gift as part of the halal source, unless you are making da`wah to this person and you think that by refraining from accepting his gift he would give up the haram thing and repent to Allah.
3. The third case, which should be clarified here, is that not all bank transactions are haram. Even in riba-bank transactions, the riba does not get in all dealings. So, a person who works for the bank has halal and haram money in his salary. If this is the case, then you are not allowed to generalize the ruling (hukm) and render the whole money of that person as haram. You can still accept his gift.
In conclusion, we’d like to state that one can approach this person and advise him/her gently and kindly if he is involved directly in the forbidden activity of giving riba-based loans. While approaching him, you can make use of the following Fatwa issued by Dr. Monzer Kahf, a prominent economist and counselor, who states:
“It is permissible to work in any department in a conventional bank, credit department or others, as long as you do not prepare any interest-based contracts or sign them on behalf of the bank.
This is the opinion of the greatest Shari`ah scholar of our time, the late Sheikh Mostafa Al-Zarqa (died 1999), and Sheikh Al-Qaradawi, Sheikh As-Salami of Tunisia and Sheikh Al-Dhareer of Sudan. The argument is that such jobs in conventional banks are not included in the wrath of Allah that is mentioned by the Prophet (peace and blessings be upon him) on the giver of riba, its taker, its writer and its two witnesses (Reported by Muslim). Besides, a prohibition of working in banks places unnecessary inconvenience and hardship on Muslims both in the Muslim majority countries and Muslim communities of other countries.”