Ratification
It is open to the principal to ratify an unauthorised agreement entered into by an agent. Ratification means that after the unauthorised act, the principal may agree to that act making it binding on the third party. Note that the third party is not bound to the agreement created by an agent with ostensible authority until the principal has ratified it. Whereas in the situation of an act done under ostensible authority, the principal is automatically bound to the third party.
Read more about this topic: Apparent Authority