Ruling 1831 — The One-Fifth Tax (Khums)

If lawful property becomes mixed with unlawful property and one knows the quantity of the unlawful property – irrespective of whether it is more or less than khums – but he does not know who its owner is, he must give away that quantity with the intention of ṣadaqah on behalf of its owner. And the obligatory precaution is that he must first obtain permission from a fully qualified jurist.