What is the religious ruling on eating from the money of a friend when it is thought that his father's money is not halal?

Merely hearing that your friend's father's money is unlawful does not obligate you to refrain from eating from it. However, if it is proven that it is unlawful, and your friend has other lawful money, then there is no harm in eating from his money or accepting his gift. But if all his money comes from his father's unlawful money, then it is not permissible to eat from it or accept his gift. If his father's money is mixed between lawful and unlawful, it is recommended to refrain from eating from it, but not obligatory.

In the case where all the father's money is unlawful and the friend has no other money, and you have eaten from it, you must repent to Allah and spend the value of what you ate on Muslim welfare. The principle is that unlawful money does not enter the ownership of its possessor, and he is obligated to return it to its owner or spend it on Muslim welfare if the owner is unknown.

Whoever deals with the possessor of unlawful money in the very unlawful money, knowing its unlawfulness, has sinned and is obligated to guarantee it, as mentioned by Ibn Rushd. It is not permissible to buy from him, trade with him, eat from him, or accept his gift for one who knows of this, and whoever does so is like a usurper.