How is the zakat calculated for a commodity that a person hands over to another for trading, on the condition that the profit is shared between them? And does the owner of the commodity pay zakat on the purchase price plus half the difference between the purchase and sale prices, or does he pay zakat on the full sale price?

The zakat on trade goods is to be paid from the goods offered for sale and their profits. It is calculated based on their market value when the hawl (one lunar year) is completed.

Regarding the zakat on a mudaraba (profit-sharing) commodity before it is sold and divided: The preponderant opinion is that the capital owner pays zakat on the principal capital and his agreed-upon share of the profit. The share of the mudarib (agent/worker) is not included in this calculation.

As for the mudarib's share of the profit, its zakat becomes due after the division of the wealth, provided his share reaches the nisab (minimum threshold) and a hawl has passed over it.

Ibn Qudamah stated that the owner of the capital pays zakat on the mudaraba profit because the hawl of the trade profit follows the hawl of its principal, and the mudarib's share is not owned by the capital owner.

Ibn Uthaymeen mentioned that the mudarib's share of the profit has no zakat on it because it acts as a protection for the capital, whereas the owner's share of the profit is subject to zakat because it is a تابع (subordinate) to a مستقر (stable) principal.