Is the authorization of Al Ahli Islamic Bank to purchase a commodity for a client and sell it to him, then give the client cash in return for it, considered usury or permissible?

If you authorize an Islamic bank to purchase a commodity and then sell it to you, there is no objection to that, even if the bank takes a fee for carrying out the task. However, if you do not have cash and wish to purchase a commodity through an Islamic bank to sell it, this is a Murabaha transaction. If the purchase is conducted in the religiously permissible manner explained in Fatwa no. 30808, then there is no objection to you authorizing the bank to sell it and give you its price.