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Once the underlying principle of this issue is understood, a ruling established on the basis of a cause ceases when that cause ceases. Thus, since wine’s intoxicating potency is what makes it forbidden and impure, it becomes pure when that potency disappears through Allah’s action—not when it is deliberately removed by human intervention, according to the correct view. As Umar ibn al-Khattāb, may Allah be pleased with him, said:

“Do not consume vinegar made from wine unless Allah Himself began the wine’s souring.”

There is no blame on a Muslim for purchasing wine vinegar from the People of the Book unless he knows that they deliberately caused the wine to sour. This is because keeping wine is forbidden. Whoever keeps it with the intention of turning it into vinegar has committed a forbidden act, and a forbidden act cannot be a means of making something lawful and permissible. But whoever keeps it to drink and use as wine does not intend to turn it into vinegar. If Allah turns it into vinegar, this is a punishment that brings about the opposite of what he intended. Thus, no harmful consequence results from its being lawful and pure.

As for other impure substances, it is permissible to cause them to break down deliberately, since doing so is not forbidden. Likewise, someone who drinks them is not subject to a prescribed legal punishment, because there is no fear that approaching them will lead people into what is forbidden, as there is with approaching wine. For this reason, the majority of scholars permit the tanning of