Is it permissible to take back a loan from a man most of whose wealth is haraam?
Question

                Is it permissible for me to take my right to take my money and other things (that I lent to him) back from a person most of whose wealth is haraam? If it is not permissible, how can I get my dues?.
Praise be to Allah.
      Haraam wealth is of two types: 

    1.That which is haraam because of 
    the way in which it is acquired, such as that which is taken by means of 
    riba and haraam transactions.

    2.That which is haraam in and of 
    itself, such as stolen and usurped wealth.

    It is permissible for you to take your right from the former, 
    because its being haraam applies to the one who acquired it only; in your 
    case, you are taking it by legitimate means. 

    In the case of the latter, it is not permissible to take 
    anything of it, because it is property that does not belong to the one who 
    stole it or usurped it; rather it belongs to its rightful owner and must be 
    returned to him. 

    Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 
    That which is haraam because of the way in which it was acquired is haraam 
    for the one who acquired it, such as riba. If the person who dealt with riba 
    dies, his wealth becomes permissible to his heirs. But as for that which is 
    haraam in and of itself, such as alcohol [i.e., if a person died and left 
    behind alcohol], then it is haraam for the one who carries it and the one to 
    whom it is carried. Similarly what is haraam remains haraam, such as usurped 
    and stolen wealth. If a person steals money then dies, it does not become 
    permissible for the heir, and if its real owner is known he should give it 
    to him; otherwise he should give it in charity on his behalf. 

    End quote from Liqaa’aat al-Baab al-Maftooh, 10/27 

    See also the answer to question no.
    13503 

    And Allah knows best.