Is it obligatory to return money taken from someone who works in insurance companies, and is it permissible to do so without his knowledge?

It is permissible to eat at the home of someone who works in prohibited insurance if they have lawful wealth from other sources. The sin falls solely upon the earner, not upon the one who takes from them through permissible means. This is evidenced by the Prophet’s — prayers and peace be upon him — dealings with the Jews and his eating of their food, even though they consumed illicit gains and practiced usury. However, if their work is solely in prohibited insurance and they have no other lawful wealth, then piety dictates avoiding dealings with them and not eating at their home.