Accepting gifts and donations from haraam wealth

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.