Is a Mudharabah contract valid if the profit share is referred to another known individual's share?

Primary text

If the principal states, 'Take this, and you shall have the like of what was stipulated for so-and-so,' and both parties are aware of that known share, the contract is valid because they referred to a known quantity between them. If they are unaware of the amount, or if only one party is unaware, the Mudharabah is void due to uncertainty.