What is the liability of an agent (Wakil) who violates the principal's (Muwakkil) instructions in a purchase?
Chapter on Selling the Musarrah (Animal with milk retained in udder)
Al-Mughni
Book of Sales
Primary text
If an agent deviates from the principal's mandate by purchasing something other than what was instructed, selling what was not authorized, or buying something other than what was specified, the agent is liable for any loss or destruction incurred to the owner's property because the agent stepped outside the bounds of trust and became akin to a usurper.
Supporting text
If the agent buys the item using his own personal credit (dhimma) and the principal later approves the transaction, the purchase becomes valid, and the obligation to pay falls upon the principal. If the principal does not approve, the obligation falls upon the agent. This ruling applies specifically when the purchase is made on credit. If the purchase was made using the principal's specific identifiable funds ('ayn al-mal), the purchase is void.