Can I eat in the home of a friend, whose wife works in a bank?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Dear inquirer!

If your friend depends only on his wife's ill-gotten money to buy food, then it is unlawful to eat their food according to the opinion of most scholars. One is required to seek lawful food and to avoid doubtful matters.

Abu Hurayrah narrated that the Prophet said: “O people, Allah is Tayyib (which implies pure), and He accepts only that which is pure. Allah has commanded the believers as He commanded the Messengers, by saying (what means): {O messengers, eat from the good foods and work righteousness. Indeed, I, of what you do, am Knowing.} [Quran 23:51] He also says (what means): {O you who have believed, eat from the good things which We have provided for you...} [Quran 2:172] He, sallallahu ‘alayhi wa sallam, then mentioned a man who travels a long distance with his hair disheveled and covered in dust, then he raises his hand towards the sky (and supplicates Allah), 'O Lord, O Lord,' while his food is unlawful, his drink is unlawful, and his clothes are unlawful and his nourishment is unlawful. How then would his supplication be accepted?” [Muslim]

On the other hand, if some of their (your friend and his wife's) property is lawful and most of it is ill-gotten, then it is detested to eat their food according to the opinion of most scholars; some scholars believe it is forbidden.

However, if your friend receives lawful income that equals or exceeds his wife's income, it appears to us that it is lawful to eat their food unless you are sure that such food is bought with the ill-gotten money.

Allah knows best.