He answered:

Praise be to Allah. If declining would cause harm—such as severing kinship ties, damaging relations, or the like—then he should accept the invitation. Maintaining kinship ties and harmonious relations is obligatory; if this can only be achieved by accepting, then accepting becomes obligatory, and doing so is not forbidden.

Alternatively, it may be said that the benefit of accepting outweighs the feared risk of involvement in what is doubtful.

If, however, declining entails no harm, but instead offers the benefit of shielding him from what is doubtful and discouraging the host from the small amount of wrongdoing involved, while accepting offers only the benefit of responding to the invitation and entails the harm of involvement in what is doubtful—which consideration carries greater weight? I believe there is disagreement on this. This issue has many subsidiary cases, a number of which have been discussed by the scholars of our school and others. Some scholars may give greater weight to abstention and religious scrupulousness, while others give greater weight to obedience and the benefit involved.

He—may Allah Most High have mercy on him—was asked:

A man has wealth derived from both lawful and unlawful sources. Is it permissible for someone to eat from his food or not?

He answered:

If he can identify the unlawful portion, he must certainly not eat from it. If he cannot identify it, eating from his food is not forbidden. However, if much of his wealth is unlawful, it should be avoided out of religious scrupulousness. And Allah knows best.