What is the ruling on zakat for gold that was sold in installments, given that the due date (hawl) for each piece cannot be recalled, and more than 13 years have passed since all the gold was sold?

If gold is in the form of jewelry for permissible use, then there is no zakat on it according to the majority of scholars. However, if it is for saving, then zakat is due on it if it reaches the nisab (eighty-five grams) and a full year has passed over it. Zakat is a debt that must be paid, for "Allah's debt is more worthy of being paid." If the exact amount is not known with certainty, one must make an effort to determine it and pay zakat on what is certain or highly probable to have completed a full year. There is no zakat on what has not completed a full year.