Here in Britain, some Muslims collect their money through lawful and unlawful means,
as they are traders and their commodities include Khamr (intoxicant) and pork meat. They are not all the same, for some of them gain most of their money unlawfully while others make just a small gain from them. Is it permissible for us, (Part No. 16; Page No. 182) as Muslims, to mix with them and eat their food when they invite us? Is it permissible to accept their donations for the Masjid (mosque)?
It is your duty to advise them and warn them of the evil end of trading in Haram (unlawful) commodities and making unlawful gains. You should cooperate with other righteous Muslims in reminding those traders of Allah's Torment for those who disobey and oppose Him by committing what He has made unlawful. Tell them that the enjoyments of this world are nothing compared to the everlasting joys in the Hereafter. If they comply, all praise be to Allah and they are your Muslim brothers. You should also guide them to return rights to their owners, if they know them, and to follow up a bad deed with a good one, may Allah forgive them and exchange their bad deeds with good ones. In this case, it is permissible for you to mix with your brothers, eat their food and accept their donations in different charitable ways such as building and furnishing Masjids and the like. By performing Tawbah (repentance to Allah) and exerting all efforts to return the rights to those they are due, Allah will forgive their past sins. Allah (Glorified and Exalted be He) says about loan sharks:
So whosoever receives an admonition from his Lord and stops eating Ribâ (usury) shall not be punished for the past; his case is for Allâh (to judge)
If they refuse to follow your advice and insist on committing (Part No. 16; Page No. 183) these unlawful deeds, you will have to abandon them for Allah's Sake, decline their invitations and accept no donations from them, as a means of disapproving of their deeds and hoping they will be deterred and will abstain from their evil acts. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.