If you are sure that a part or percentage of the income is from unlawful source, the situation can be :
A. If you know the percentage or quantity of the unlawful funds, then you must take that unlawful part away and give it back to its real owner or if the real owner is unknown to you then to give it as Majhool Al-Maalik (funds of unknown owner) which is given to the Marje' of Taqleed to distribute it among the poor on behalf of the real owner.
B. If you do not know the exact percentage of the unlawful money or items, but you estimate it to be less than 20%, then you must pay the Khums of the whole amount, which will make the remaining amount allowed.