All perfect praise be to Allah the Lord of The Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
It isn`t wise to break ties with one`s brother because the latter persists in committing sin; rather one should visit him on regular basis and keep reminding him that he should quit that sin and maybe he might respond. Moreover, he shouldn`t be left to bad friends who would only encourage him to commit sin. He should also be reminded that Allah forgives all sins except ascribing partners in worship with Him. This is in order to make him ponder on his situation and start holding himself to account.
Jurists have stated that it is permissible to engage in business transactions with one whose wealth is mixed with lawful and forbidden earnings, accept his gifts and eat from his food. The evidence on this is that the Prophet of Allah (PBUH) accepted the gifts of the Jews and ate their food although Allah Said about them {What means}: " (They are fond of) listening to falsehood, of devouring anything forbidden." {Al-Mai`dah, 42}.
Therefore, when a man came to Ibn Mas`oud (May Allah be pleased with him) and said to him: "I have a neighbor who accepts usury and keeps inviting me" Ibn Mas`oud replied: "Food and drink that he offers you are lawful to you, but he is liable for the sin." {Musanaf AbdulRazaak, vol.42/pp.150}.
Our jurists, Shafie, stated in several places of their Fiqh books that it is permissible to engage in business transactions with the person whose wealth is mixed with lawful and forbidden earnings.
It is stated: "It is permissible to engage in business transactions with the person whose wealth is mixed with lawful and forbidden earnings and the same goes for eating his food and accepting his gifts. This is to the exclusion of wealth which one is absolutely certain that it is unlawful and whoever wants to avoid dealing with such person is at liberty to do so." [Hasheyat al-Qhalubi, vol.4/pp.263]
As for the ruling of Sharia on working in usurious banks, it has already been given in Fatwa No.(
467). And Allah The Almighty Knows Best.