What is the ruling on working in companies and institutions of a special nature, such as five-star hotels and foreign banks, and companies whose source of funds is suspect? And is it permissible to accept gifts from relatives and individuals who deal with usury or work in usurious institutions?

There is no objection to guarding foreign companies if their core business is permissible in Islamic law, because the jurists permitted a Muslim to hire himself out to a disbeliever for a specific task, as 'Ali (may Allah be pleased with him) did with a Jew. As for dealing with those whose wealth is mixed, containing both lawful and unlawful elements, it is permissible. The general principle is that people's wealth is permissible unless it is known to be unlawful. The Prophet (peace be upon him) and the Companions dealt with the Jews despite their consumption of usury and ill-gotten gains. Al-Shafi'i stated the permissibility of buying and selling with someone whose wealth is mixed with lawful and unlawful elements, as long as it is not known that the money itself is specifically unlawful.