Answered by Shaykh Faraz Rabbani
What is the hukm regarding things received from another which were acquired with unlawful money? What about if this other persons money is partly lawful and partly unlawful?
There are a few possibilities here:
If the wealth of the other person is more than 50% haram, it is not permitted to transact with them or accept their gifts;
If their wealth is less than 50% haram, it is permitted;
If you know that the very item you received was acquired in a purely haram way (such as with 100% haram money), it would not be permitted to accept such an item;
When in doubt, or uncertain, we assume that the other person’s wealth is mostly halal, even if they are non-Muslims, and we can deal with them. However, whenever there is genuine reasons to doubt, it would be more cautious to avoid dealing with the person. At the same time, it is obligatory for us to have a good opinion of all, even non-Muslims, and we cannot spy on others or assume the worst of them. [Based on texts from Ibn Abidin, the Fatawa al-Hindiyya, and Ahsan al-Fatawa.]