Question:

Respected Dr., I have a friend who works with two non-Muslim brothers in the market. One of them is involved in a legitimate business—ordinary trade—and my friend works with that man. The second brother deals with both stolen and non-stolen goods. My friend receives his salary from the first brother, who has lawful goods, every week at the end of Saturday. He does not sell any stolen items, and their goods are separate. However, the brothers are partners, and their capital is combined, mixing their funds. My friend has another job, but it pays poorly. Is it permissible for him to continue working with these two brothers, or should he leave them? May Allah reward you.

Answer:

In the name of Allah, the Most Gracious, the Most Merciful.

Praise be to Allah, and peace and blessings be upon the Messenger of Allah, his family, companions, and those who follow him. As for what follows:

There is no harm in your friend continuing his association with these two brothers as long as his work is confined to the one engaged in lawful trade. The mixing of the two types of money does not affect him because money itself is fungible, and the prohibition does not extend to the actual money earned through unlawful means but pertains to the liability. This is unless the money is prohibited in itself, such as alcohol, pork, and the like. Allah, the Exalted, knows best.

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Taken from fatawaalsawy.com