My wealth was deposited in a usurious bank. When I knew that this constitutes usury, I decided to withdraw it from the bank, get rid of the interest in charity and deposit the capital in an Islamic bank. What I want to ask about is: throughout the past ten years, I used to pay the Zakaah from my salary (which is lawfully earned) for the total value of this deposit including the interest. Now, I realized that no Zakaah should be paid for the usurious interest but it is only due upon the capital. The question now is: what is the ruling on the portion of Zakaah that was paid for the usurious interests throughout the previous ten years. Is it permissible for me when getting rid of the interest to keep an amount that equals this sum and add it to the capital that I will keep (instead of the portion I used to pay in Zakaah for the usurious interests) since I used to pay it from my lawfully earned salary and there was no Zakaah due for these interests?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

What you should have done concerning the presented matter is to pay Zakah for the original deposit. The usurious interest is an unlawful sum of money that should not be owned and consequently no Zakah should be paid for it. One should get rid of it in full by spending it to serve the general interests of Muslims.

Anyway, since you paid a sum of your money with the intention of Zakah then you discovered that you were not required to pay it; you have the right to consider this sum as part of the Zakah of your money for the coming year unless you volunteer. That is to say that when you pay the Zakah of your money next year, calculate what you mistakenly paid from the total sum of the Zakah due from you. In this context, scholars said: "If the one collecting Zakah takes more than the due sum, this excess should be counted from the Zakah of the coming year. If he takes less than the sum believed to be due by the owner; the owner is obliged to pay the remaining sum between himself and Allaah The Almighty." This was mentioned by the Hanbali scholar Ibn Muflih . The entire interest is forbidden and it should be spent on the poor, the needy, the orphans and the like.

Allaah Knows best.