Dealing with a Riba Practitioner and Responding to His Invitation to a Wedding Feast

Question:
Honorable Shaykh, what is the ruling on dealing with a person who deals in riba (usury or interest)? And is it permissible to attend and respond to his invitation if he invites you to a wedding feast or the like?

Answer:
If all his wealth is from riba, it is not permissible for you to eat from his food or respond to his invitation. However, if his wealth is mixed from what is lawful and what is forbidden, there is no harm in responding to his invitation, because you do not know whether this wealth is from the forbidden or from the lawful. The Prophet (peace and blessings be upon him) responded to the invitation of a Jew and ate from his food, even though the Jews deal in riba. So if you are not certain that this wealth is forbidden, there is no harm; the default is permissibility. But if you are certain that this wealth is forbidden, it is not permissible for you to eat from it.