Is it permissible for the owner of capital to withhold the profits of a specific transaction from his partner who contributes effort, claiming that the owner of capital contributed both the effort and the money to this transaction, while the partner states that he participated at the beginning of the transaction?

The mentioned company is a permissible Mudarabah (definition) (profit-sharing) company. Regarding the transaction conducted by the Rabb al-Mal (investor), the ruling depends on knowing whether his action was with the permission of the 'Amil ( Mudarib/agent) or on his own initiative, whether the transaction involved goods or cash, whether the capital for the transaction was all of the capital or only a part of it, and whether it was before or after the 'Amil's action. What happened must be clarified to determine the Shar'i (Islamic legal) ruling.