What is the procedure and legality of a master dissolving a manumission contract (Kitabah) when the enslaved person defaults (ajz)?

Primary text

If two installments are due and the enslaved person defaults on both, and the master chooses to dissolve the contract and return the person to slavery, this is permissible without the presence of a judge or sovereign authority, nor is it necessary to appoint an agent for this action. This ruling is supported by the action of Ibn Umar, and it is the view of Sharih, Al-Nakha'i, Abu Hanifa, and Al-Shafi'i. The evidence supporting this includes the report by Sa'id, through his chain of narration from Ibn Umar, that he returned an enslaved man to slavery after he paid 900 out of 1000 dinars and defaulted on the remaining 100. Another narration shows Ibn Umar returned his slave to slavery after he paid 10,000 out of 20,000 and then reported that he had traveled through Iraq and Hijaz and wished to return to slavery. Furthermore, the Prophet, peace be upon him, stated: 'Any man who contracts with his slave for one hundred ounces and he defaults on ten ounces, he is a slave.' The dissolution is justified because the contract was based on an exchange for which the debtor defaulted, granting the rightful owner the power to dissolve it, similar to when the subject of a forward sale (Salam) cannot be delivered. Moreover, since this is a dissolution of an agreed-upon contract, it does not require a judge, similar to the dissolution of a freed woman's marriage under a slave.