Praise be to Allaah.
Before the sale there was no zakaah on it, because it was not
trade goods. After selling it, the zakaah is zakaah that is due on a debt.
In other words, when he receives an instalment, he should pay zakaah on it
for that year; when he receives another instalment in the second year he
should pay zakaah on it for two years; when the third year has passed, he
should pay zakaah for three years, and so on. End quote.
Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him).
Liqaa’aat al-Baab al-Maftooh (2/34).