Is it permissible to invest a person’s money, whose source is known to be unlawful (haram), in a permissible (halal) project?

One must avoid unlawful money or money that is questionable. If it is highly probable that most of a person's money was acquired through unlawful means, then it is not permissible to invest that money for them, because it would be an affirmation and complicity in their possession of unlawful money, and the profits would be from unlawful money. However, if the proportion of unlawful money is small, then there is no objection to investing it. The owner of the money is advised to dispose of what they acquired unlawfully, by returning the money to its rightful owners if possible, or by giving it as charity on their behalf, or by spending it on charitable causes and for the benefit of Muslims if it was from usurious gain or gambling.