How can one dispose of haram money earned from working in an interest-based bank for nine years, which was then invested in a permissible project that generated significant profits, and must one dispose of only the principal, or does that include the profits resulting from the project?

The questioner is congratulated on his repentance, and we ask Allah to grant him success. Regarding money earned from unlawful work, Shaykh al-Islam Ibn Taymiyyah held the view that if someone acquired unlawful money out of ignorance of its unlawfulness, it is permissible for him to consume it after becoming aware. However, if he knew of its unlawfulness and disposed of it, then he must donate it as charity. As for money that is inherently unlawful, such as the dowries of prostitutes or the price of alcohol, it is not permissible for the recipient, and it must be spent on the welfare of Muslims. If the poor person who acquired this money repents, it is permissible to give him from it according to his needs or as capital for his work.

Based on this, if the questioner was ignorant of the unlawfulness of his work in the bank and then left it, the money he earned is not considered unlawful. However, if he knew of its unlawfulness while working, then the money is not permissible for him. If he has money or a craft that suffices him, he must spend the money on the welfare of Muslims. If he has no money or ability to earn, he should be given from it what he needs. If he is capable of earning, he should be given from it what can serve as capital for him. The questioner must clarify his situation to know the ruling on his money and profits. As for the profits arising from investing this unlawful money, the most just approach is to divide it equally between the capital and the worker.