Is a fixed monthly amount from the profit—as paid by the partner—considered doubtful?

The agreement reached is a Mudarabah (profit-sharing partnership) in which it is not permissible to specify a fixed, known profit for the capital owner. Instead, the capital owner should receive a percentage of the profit. If there is no profit, the capital owner receives nothing. Therefore, if the agreement is for a percentage of the profit, such as half or a third, there is no objection. However, if the agreement is for the worker to pay the capital owner a fixed, known amount every month, then it is an interest-based loan (riba) and not a Mudarabah. In the event that the Mudarabah contract is deemed invalid, the entire profit belongs to the capital owner, and the worker receives a wage equivalent to what a person of his caliber would earn (ujrat al-mithl), or a profit equivalent to what a person of his caliber would earn.