Is it permissible to deal with an interest-based bank to obtain interest-free installment purchase facilities for necessities, knowing that the Islamic bank does not offer them? Is it also permissible to open a current account with it for deposits and interest-free transfers to obtain additional facilities, and what is the ruling on transferring a portion of one's salary to it to pay the monthly installments? And does the rule "the unlawful does not prevent the lawful" apply to this case?

It is not permissible to deal with usurious banks except out of necessity or a recognized need, because any dealing with them is considered aiding in sin and aggression. The resolution of the Islamic Fiqh Academy stipulated the prohibition of dealing with usurious banks when an Islamic alternative exists. The facilities offered or the absence of direct interest do not permit dealing with these banks, as every dealing with them is forbidden, even if it does not involve direct interest but rather benefits from the movement of the account and money. The rule "the forbidden does not forbid the permissible" is not suitable for use as evidence here, because any transaction with these banks, even if permissible in its form, aids in sin and strengthens the people of falsehood, and thus it cannot be described as permissible. The one who consumes usury, its giver, its scribe, and its two witnesses are cursed, and similarly, everyone who aids in a forbidden act, like drinking alcohol, is cursed. If people refrained from dealing with usurious banks, their transactions would be Islamicized.