What is the ruling on a transaction that involves investing a sum of money in the foodstuff trade, with the condition of not specifying a fixed interest rate, and an agreement on a monthly percentage of the profits?

This transaction is called Mudarabah (definition) or Qirad, and it is a permissible type of partnership, where one party contributes their effort and labor, and the other contributes their capital. The profit is then shared between them according to an agreed-upon, undivided percentage at the beginning of the contract.