Is an oath not to wear the master's clothing or ride his mount broken by using the slave's clothing or mount?

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If a person swears not to wear the master's clothing or ride his mount, and then wears the slave's clothing or rides the slave's mount, the oath is broken. This is the view of Al-Shafi'i. The reasoning is that both the slave's clothing and mount are owned by the master, thus the oath-taker's act falls under the scope of the oath, similar to the ruling concerning the master's house.