What should I do with money that was mixed with usurious interest and that I spent, while regretting that action?

"Interest is usury (riba), which Allah has forbidden and whose devourer He has warned with war. The Prophet, peace and blessings be upon him, cursed theaker of usury, its consumer, its scribe, and its two witnesses. Whoever receives anything from usurious gains must dispose of it immediately by spending it on the poor and needy with the intention of ridding oneself of unlawful wealth. As for what was consumed before knowing its prohibition or being ignorant of it, one is not required to spend it, for 'So whoever receives an admonition from his Lord and desists, he will have what has passed, and his affair is entrusted to Allah.' Sheikh Abdul Aziz ruled that usurious money must be returned to its rightful owner if its prohibition was known at the time of its taking."