What is the ruling, in Islamic law, on investment certificates with variable income and those with fixed income?

We have clarified in previous fatwas that investment certificates with a fixed, guaranteed return are considered a usurious loan and are forbidden. This is because the depositor pays money to the bank to receive it back with an increase, which is considered usury. A Muslim must avoid them, due to the Almighty's saying: {O you who have believed, fear Allah and give up what remains [due to you] of usury, if you should be believers} [Al-Baqarah: 278], and due to the Prophet's (peace and blessings be upon him) saying: "The Messenger of Allah cursed the one who consumes usury, the one who feeds it, its scribe, and its two witnesses, and he said: 'They are all equal (in sin).'"

As for investment certificates that fall under the ruling of legitimate Mudarabah, where the owner of the capital gives his money to the bank to invest it in a project in exchange for a percentage of the profit (if a profit is made) without guaranteeing the principal or a known profit, this type is permissible to deal with and benefit from its profits.