What is the ruling on orphans' money placed in usurious banks by their guardian? Are they sinful for benefiting from its interest before knowing of its prohibition? Is Zakat retroactively obligatory on that money? Is it obligatory for them to purify it after knowing of its prohibition, citing the the noble verse: ﴿So whoever receives an admonition from his Lord and desists, he may have what has already passed, and his affair is to Allah. But whoever returns [to usury] - those are the companions of the Fire; they will abide eternally therein﴾? Is it permissible for them to spend it on public interests such as mosques and Quran memorization centers, or assisting poor families? Can it be disposed of gradually?

Islamic law differentiates between someone acting willingly and someone acting under duress or necessity, and between someone ignorant of a prohibition and someone who is aware of it. There is no blame on the questioner for what they consumed from usurious gains out of ignorance or necessity, for "whoever receives an admonition from his Lord and stops, then what has passed is for him." However, for someone who became aware of the prohibition and usurious gains were deposited into their account after this knowledge, they must dispose of these gains through installments according to their ability, by spending them on building mosques or assisting those in need. Zakat is obligatory on the wealth of orphans and minors if it reaches the nisab (threshold) and a full year has passed on it. It does not lapse with time, and it is due on the principal amount, not on the usurious gains. It is not permissible to keep money in usurious banks except out of necessity.