Is money earned from a business that originated from a forbidden usurious loan, and then its owner repented sincerely and got rid of all the illicit money, and then started his business with lawful capital, relying on the experience and reputation he gained while working with the forbidden, considered lawful or unlawful, or is there a doubt about it?

Borrowing with usury is a grave sin that necessitates repentance. The conditions for repentance are: abandoning the sin, regretting it, and resolving not to return to it. It is not a condition for repentance to dispose of money and properties acquired from a usurious loan; rather, the resolve not to return to usury is sufficient. What a person gained in experience, reputation, or knowledge during their previous work does not affect the validity of their repentance. These whisperings must be repelled because they are from Satan.