What is the ruling on obtaining Islamic financing based on the deferred sale of a real commodity, and then investing the amount in an Islamic bank in Egypt, knowing that the investment profits will be higher than the deferred price, and do the doubts raised about the legitimacy of the bank's dealings affect the ruling on investing in it?

There is no sin upon you for past investments in fixed-income government bonds, as long as you based your actions on a fatwa (definition) from someone you trusted in their knowledge. You may benefit from the profits previously earned, and you are not required to dispose of any of them. This is based on the statement of Shaykh al-Islam Ibn Taymiyyah that when a Muslim who acted based on an interpretation repents, what he considered permissible is forgiven, and what he seized becomes lawful for him. It is also based on the Almighty’s saying: "So whoever receives an admonition from his Lord and desists, he may have what has already passed, and his affair is left to Allah."

As for what lies ahead, it is obligatory to cease investing in fixed-income government bonds and to seek an Islamic bank where you can invest your money, ensuring that the investment field has no connection to unlawful matters or their ambiguities. Inquire from knowledgeable specialists in your country about the most suitable and reputable Islamic banks that adhere to Sharia (definition) regulations.