Is zakat due annually on a hoard of gold from which one-fifth (khumus) was paid as zakat upon its discovery, while its nisab (minimum taxable amount) remains intact? And if not, what is the meaning of the saying: "If gold reaches twenty mithqals, zakat becomes due"?

Zakat on gold must be paid if it reaches the nisab and a full lunar year (hawl) has passed, provided it is not jewelry used by a woman. The nisab for gold is approximately 85 grams, and the amount to be given is one-quarter of one-tenth (2.5%). If it falls below the nisab, no zakat is due on it.