What is the ruling on subscribing to social security and receiving monthly payments from it after retirement, from an usurious bank chosen by the individual? Is repentance obligatory if it is unlawful, and what is the nature of this repentance given that the social security income is the individual's sole source of income?

It is not permissible to subscribe to social security if the bank is usurious. One who is subscribed to it must cease doing so and withdraw their money, disposing of the excess by giving it to the poor and needy. The believer must be certain that their sustenance is in the hands of Allah, and that there are legitimate means of investing money. One does not know if they will live to retirement or not.