Validity of an agency instruction to take possession of a debt owed to the principal and invest it as *Mudarabah* (profit-sharing)?

Primary text

The instruction given by an owner to a man to take possession of money owed by a third party and invest it as *Mudarabah* is valid upon the recipient taking possession and commencing work. The recipient acts as an agent (*wakil*) in taking possession and is considered a trustee (*mu'taman*) over the funds. This is permissible because he took possession with the owner's permission from someone else, allowing the arrangement to immediately become a *Mudarabah*, similar to instructing an agent to take money from one's slave and trade with it.