When Zakat becomes due on an uncollected debt or a forfeited portion thereof.
Chapter on Zakat on Debt and Charity
Al-Mughni
Book of Zakat
Primary text
If a debt equal to the Nisab amount has a full year pass while uncollected, and subsequently, half of it is forfeited while the wife collects the other half, Zakat is due only on the collected half, because Zakat was established on that specific portion, and the waiver applied only to the other half. If the entire debt passes a full year before collection, Zakat is due for that single year upon collection. If several years pass before collection, Zakat is due for all those years, provided the amount remains at the Nisab level.
Supporting text
If the entire dowry is forfeited before collection due to annulment initiated by the wife's side, no Zakat is due on it, following the principle established for debts where the claim becomes unattainable without the creditor's explicit release or despair of recovery. Similarly, if the owner despairs of recovering lost wealth (Mal Dhall), Zakat is not due, as Zakat is an act of compassion (Muwasaah) due only on what has been secured.