What is the ruling on taking money from a person who deals in usury without knowing the nature and terms of his dealings with a third party, and is it obligatory to ask about the source of this money if it is one's livelihood?

The questioner is not obliged to inquire about the true nature of the transaction conducted by a person who does not shy away from taking usurious interests and gives money to another to profit for him. It is permissible for him to benefit from this person's money as long as he does not know that it is unlawful money. If his money is mixed between lawful and unlawful, then dealing with him and benefiting from his money is permissible.