What is the ruling of Islamic law regarding a dispute over adjusting the capital of an Islamic Mudarabah from 50,0 to 100,0 due to currency inflation, especially since the initial agreement stipulated that the amount was their responsibility in the local currency, and should Zakat be borne by the partner who owns the capital or by all three partners as an expense of the project?

The capital provider in a Mudarabah (definition) partnership is not permitted to demand more than what he initially paid in local currency. It is also impermissible to guarantee the capital in Mudarabah, as this is a corrupt condition.

As for zakat (definition), it is obligatory upon the capital provider for the entire capital and its profits, excluding the worker's share. This is because the worker's share is not owned by the capital provider, and a person is not obligated to pay zakat on someone else's wealth. Zakat is to be disbursed from the wealth and calculated from the profit. As for the worker, there is no zakat due on his share until the profit is divided. Once it is divided, the worker starts a new lunar year (hawl) for his zakat from that time.