What is the ruling on working as a teacher in a school that pays its teachers' salaries from the interest of its usurious deposits? Is it obligatory to ascertain the source of the money before working, and what should one do if this is the case with most schools?

Scholars have differed on the ruling concerning dealing with someone who possesses unlawfully acquired wealth, and whether money received through a void contract (such as usury) confers ownership or not. The madhhab (school of thought) of Abu Hanifa holds that it does confer ownership, while the madhhabs of Ash-Shafi‘i and Ahmad hold that it does not. They also differed on the specific designation of currency.

Those who hold that possession through a usurious contract confers ownership and that currency is not specifically designated would not rule the receipt of a salary from usurious interest as unlawful. In this case, the sin would be on the owner of the deposit. However, those who hold that possession through a usurious contract does not confer ownership and that currency is specifically designated would rule this salary as unlawful because it originates from the very essence of unlawful money.

If this is the general situation among most schools of thought, then there is no harm in adopting the first view, because a change of possession alters the ruling, as indicated by the Hadith of Barirah, where the Prophet, peace and blessings be upon him, said: “It is charity for her, and a gift for us.” Ibn Mas'ud also said concerning a neighbor who consumed usury: “Its benefit is for you, and its sin is upon him.” Ibn 'Uthaymin pointed out that money acquired unlawfully, such as through usury, is forbidden to its acquirer, but not forbidden to others if they acquire it from him through a lawful means, citing the Prophet's, peace and blessings be upon him, dealings with the Jews as evidence.