Mixed Income
Question :

Somebody had income from lawful and unlawful sources, like he took interest from the believers. He has stopped doing this now and started practicing the religion. What is his obligation in respect to this money now, considering that he does not know how much he took from who?

Answer :

If he does not know who he took the interest from, and he cannot determine which part of his wealth is lawful and which part is unlawful, then he should pay the khums from the mixed amount.