A person who has a current account in Islamic banks pays a service fee for this account
and does not receive interest for the deposited money since it is not deposited for investment; rather, it is a current savings account (Part No. 13; Page No. 429) from which the depositor can take any sum of money. However, banks use a large part of these deposit accounts in their investments without paying the owner any money. Is it permissible for banks to use the money this way given that it is left in the bank as a trust or do they have to first ask permission from the depositors?
This depends on the agreement that was made between the depositor and the bank. If they agree upon permissible transactions, it is permissible for them; otherwise, it is not permissible. Also, it is known that convention stands for spoken agreement in this concern and similar ones. Today convention dictates that by depositing his money in a bank, the depositor gives permission to the bank to invest the money as long as his money will be available whenever he demands it.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.