Accepting gifts and donations from haraam wealth
Question

                Some Muslims here in Britain accumulate their wealth from both halaal and haraam sources, because they are businessmen and some of the things in which they deal are alcohol and pork. They vary in the extent to which they do that. In some cases most of the person’s wealth comes from haraam sources, and in others only a little of their earnings is haraam. Is it permissible for us Muslims to mix with them and eat their food if they invite us? Is it permissible for us to accept their donations from this wealth for the mosque?.
Praise be to Allah.
    Firstly: You have to advise them and warn them of the evil 
    consequences of dealing in haraam things and acquiring wealth from haraam 
    sources.  You should cooperate with your brothers among the righteous to 
    remind them and warn them of the wrath of Allaah and the severity of His 
    punishment of those who disobey Him and wage war against Him by committing 
    haraam actions. You should teach them that the pleasures of this world are 
    few, and that the Hereafter is better and more lasting. If they respond, 
    then praise be to Allaah. In that case they are your brothers in Islam. Then 
    you should advise them to return that which they took wrongfully to its 
    rightful owners, if they know who they are, and to follow their bad deeds 
    with good deeds, so that Allaah will accept their repentance and turn their 
    bad deeds into good deeds. Then it will be permissible for you to mix with 
    them as your brothers in faith, and to eat their food and accept their 
    donations for building and furnishing the mosque etc., because by repenting 
    and returning to people what is rightfully theirs as much as possible, their 
    previous sins will be forgiven, as Allaah says (interpretation of the 
    meaning): 

    “So 
    whosoever receives an admonition from his Lord 
    and stops eating Ribaa, shall not be punished for the past; his case is for 
    Allaah (to judge)”

    [al-Baqarah 2:275]. 

    Secondly: 
If they still refuse to 
    heed advice and reminders, and they persist in doing haraam things, then you 
    have to forsake them for the sake of Allaah, and not respond to their 
    invitations or accept their donations, as a rebuke to them and, in the hope 
    that this will deter them from committing evil actions. 

    And Allaah is the Source of strength.