Regarding the Ḥuqúqu’lláh … this is applied to one’s
merchandise, property and income. After deducting the necessary
expenses, whatever is left as profit, and is an addition to one’s
capital, such a sum is subject to Ḥuqúq. When one has
paid Ḥuqúq once on a particular sum, that sum is no
longer subject to Ḥuqúq, unless it should pass from one
person to another. One’s residence and the household furnishings are
exempt from Ḥuqúq. Ḥuqúqu’lláh is
paid to the Centre of the Cause.
(April/May 1927, written on behalf of Shoghi Effendi to an individual believer, translated from the Persian)