Is the fixed rate of 12% of the annual profits that the questioner takes from his wife's money, which her father manages, permissible or forbidden?

Stipulating a percentage of the capital in a Mudarabah contract renders it invalid, because one of its conditions for validity is that both parties agree on a fractional share of the profit for each. If the Mudarabah becomes invalid, then all the profit belongs to the capital owner, and the worker receives either a wage comparable to his work (ujrat al-mithl) or a profit comparable to it, regarding which there is a difference of opinion among jurists.