What is the ruling regarding the preemption right of a slave authorized for trade (Ma'dhun lahu fi al-tijarah)?

Primary text

The slave authorized for trade has the right to claim preemption because he is authorized for purchasing. However, if he waives the right, his waiver is not effective because ownership belongs to the master, and the master did not authorize him to invalidate his rights. If the master waives the right, it lapses, and the slave cannot claim it, because the master has the authority to restrict him, and because the right has been waived by its rightful owner, it lapses upon that waiver.