Book of Zakāt
Introduction
...
Book of Zakāt
Zakāt becomes obligatory when five conditions are met: freedom, Islam, ownership of the nisāb (minimum taxable amount), stability of that ownership, and the passage of one lunar year—except in the case of ʿushr-crops⦗1⦘. The offspring of pasturing livestock and commercial profit are likewise exempt from the one-year stipulation even if they do not themselves reach a nisāb; their year follows that of their original capital—if the principal already constitutes a nisāb, its year is counted, otherwise the count begins once the nisāb is completed.

Anyone to whom a debt—or any entitlement such as a dowry—is owed, whether the debtor is solvent or insolvent, must pay zakāt on it for the past years when he actually receives it. No zakāt is due on the property of someone whose outstanding debt reduces his wealth below the nisāb, even if the assets are outwardly apparent; an expiation (kaffārah) is treated like any other debt.

If a person acquires a full nisāb consisting of young animals, the year starts from the moment of acquisition. Should the nisāb drop below the threshold during the year, or should he sell it or exchange it for property of a different genus without intending to evade zakāt, the year is interrupted. If, however, he exchanges it for property of the same genus, he continues counting the original year.

Zakāt is due on the very property itself, yet it also attaches as a personal liability. Its obligation is not subject to the owner’s ability to pay nor to the continued existence of the property, and in an estate zakāt is treated like any other debt⦗2⦘.