What do the respected scholars say regarding the following issue: Those people who deposit money in banks and take profit at the rate of 5% or more on that amount—which is interest (riba)—claim that since zakah is deducted on that money, it therefore becomes permissible. Is it permissible to eat and drink in the homes of such people or to establish marital relations with them, even if they are very close relatives?
If the total or predominant income of such people is derived from this kind of unlawful (haram) source, then eating and drinking in their homes is Islamically impermissible (ḥarām) and must be strictly avoided. However, even in the case where their lawful (halal) income is predominant, exercising caution is still better. The same ruling applies with regard to establishing marital relations with them.
كما في الفتاوى الهندية: ولا يجوز قبول هدية أمراء الجور لأن الغالب في مالهم الحرمة إلا إذا علم أن أكثر ماله حلال بأن كان صاحب تجارة أو زرع فلا بأس به لأن أموال الناس لا تخلو عن قليل حرام فالمعتبر الغالب وكذا أكل طعامهم كذا في الاختيار شرح المختار اھ (5/ 342) والله اعلم بالصواب