What is the Shar'i (Islamic legal) evidence for the general principle of "necessities permit the forbidden," and can it be used to justify dealing with an usurious bank in cases of necessity, given that the Quranic verses relied upon for this principle were revealed in the context of food?

The rule "necessities permit the forbidden" means that what is forbidden becomes permissible when there is a necessity that requires committing it, such as eating carrion for one who is compelled. This also includes the dropping or alleviation of obligations. This rule is supported by Quranic verses like: {But whoever is compelled, without desiring it or exceeding due limits – then there is no sin upon him}, prophetic traditions, and the general evidence of the ease of Sharia and the removal of hardship. Jurists have unanimously agreed upon this rule and have acted upon it in all rulings, such as the permissibility of dealing with riba-based banks in cases of extreme necessity when no alternative exists. The lesson is in the generality of the wording of the verses, not in the specificity of their reason for revelation.