What is the ruling on money acquired from the interest of traditional banks, which I recently learned is impermissible, after depositing the money for four years, and how can the money be purified from it, knowing that I do not know its value, and is it permissible to deposit money in an Islamic bank?

A Muslim is required to seek out what is lawful, and it is not permissible for him to deposit his money in interest-based banks except out of necessity and in an account that does not accrue interest. This is due to what has been narrated from the Prophet, peace and blessings be upon him, who cursed the one who consumes usury, the one who feeds it, its two witnesses, and its scribe.

Therefore, the money must be withdrawn from the interest-based bank immediately, and the usurious interests that accrued after knowing their prohibition must be disposed of by spending them on Muslim welfare or for the poor and needy. As for what was earned from interest before knowing its prohibition, some scholars are of the opinion that it is not necessary to dispose of it, 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 to Allah.﴾

The accrued interests can be identified by referring to the account statement.

As for depositing money in an Islamic bank for investment, there is no harm in it, with the necessity of seeking out the banks most committed to Sharia compliance.