What is the ruling on taking the money of a participant who voluntarily withdrew from the fund, based on a prior condition that the amount paid is non-refundable and considered a donation to the fund?

This fund is a partnership contract. Any partner may withdraw from it whenever they wish, provided that it does not harm the other partners. They shall recover their capital along with their share of the profit, or their share of the loss shall be deducted. The condition of depriving a partner of their capital upon withdrawal is invalid because it contradicts the intent of the Sharia and constitutes devouring people's wealth unjustly. It also contradicts the essence of the contract, which is based on sharing profit and loss. If the partnership becomes void, the profit and loss shall be distributed according to the capital contributions of the partners.