How is the agency terminated if the principal disposes of the item the agent was authorized to sell?

Primary text

If an agent is authorized to sell a specific slave, and the principal subsequently manumits the slave, sells him in a valid sale, enters into a contract of manumission through payment (mukātabah), or arranges for deferred manumission (tadbīr), the agency is voided. This is because the principal no longer possesses ownership, thus eliminating the basis for authorizing disposition over that property. In the case of mukātabah or tadbīr, some opinions state the item is no longer subject to the original sale mandate; others hold that the principal's action demonstrates intent to retract the order for sale. If the principal executes an invalid sale of the slave, the agency remains valid because ownership was not transferred.