What is the ruling on capital acquired from work that involves a mixture of what is lawful and unlawful, if one wishes to start an independent project with this money?

If the enquirer acts upon a fatwa permitting the utilization of money acquired by mistake, believing it to be correct, then he is excused, and the sin of the fatwa falls upon the mufti if he erred. It is permissible for the enquirer to utilize this money in an independent project. If the project becomes profitable and doubts dissipate, he may then, as a precaution, set aside an amount equal to that money.