Is it permissible to advise someone to abandon bank interest while retaining what has already been received from usurious funds?

If a person was ignorant of the prohibition of usury, then came to know the ruling and ceased [from it], there is no blame upon him for benefiting from the profits he acquired before gaining knowledge, due to 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." (2:275) However, if he was aware of the prohibition of these interests, it is not permissible for him to benefit from them.