What is the ruling on buying and selling shares of Islamic banks?

If banks call themselves "Islamic" to deceive people and deal in usury or prohibited transactions, then it is not permissible to contribute to them or trade in their shares, because that constitutes aiding in sin. However, if they are truly Islamic and adhere to the texts of the two revelations (Qur'an and Sunnah) and do not engage in prohibited transactions, then there is no harm in contributing to them and trading in their shares; in fact, it is commendable to encourage them. The "Fatwas of the Permanent Committee" have stipulated the prohibition of contributing to usurious banks and its permissibility in non-usurious banks, while emphasizing the obligation to dispose of usurious profits by spending them on charitable causes.