What is the ruling if the husband authorizes an agent for Khul' using money, but the agent performs Khul' using an item of a different kind (e.g., a slave)?
General Chapter
Al-Mughni
Book of Khul' (Redemption Divorce)
Primary text
If the agent deviates from the stipulated kind of compensation, such as being commanded to use money but concluding the Khul' using a slave, or vice versa, or if the agent is commanded to perform it immediately but contracts for deferred compensation, the Khul' is invalid. This is because the agent deviated regarding the kind of compensation, which invalidates the transaction, similar to an agent in a sale. Furthermore, the subject matter of the exchange is not owned by the husband, as he did not authorize it, nor is it owned by the agent.
Supporting text
The view of Al-Qadi suggests that the compensation specified by the husband should be binding on the agent, and the agent retains what was received in the exchange, analogous to the case of differing in amount. This is countered by observing that this invalidates the agent in sale, and because this is a Khul' the husband did not permit, making it invalid as if no agency existed.