What should a person do who has taken out an interest-based loan and is still paying it back, in order to cleanse himself of his sin, knowing that he has a business based on this loan, and what remains of his salary is not enough to cover the loan payments and his household expenses?

If a person takes out an interest-bearing (riba-based) loan, they have committed a great sin, and they must repent and resolve not to return to it. As for investing this money in trade or the like, it is permissible, and the profits generated from it are lawful. He is not obliged to dispose of the principal of the loan or its profits, because the sin is attached to his conscience, not to the money. If there is a benefit in expediting the repayment of the loan, such as the waiving of interest, then he should proceed with it; otherwise, there is no need to expedite the repayment.