Islam prohibits the earning or giving of interest on saving or investment. This creates problems in economic systems which is built on interest based finance.

If a Muslim has deposited his money in a interest bearing account, or the interest has come to his account without his choice or intention, he should return the money to the source [provided that the source is someone other than an institute; such as the bank and provided that the source can be traced]. If however, the source cannot be traced or the source of the interest money is some institute such as the bank, then the interest money should be given away to the poor without any intention of reward.

It is incumbent upon you to give the interest money from the bank as charity to the poor who are entitled to receive Zakah.

Also included under this heading are earnings which are generated by not only the sales of haram items, but also halal items acquired through haram means.