What is the ruling regarding the ability of a slave who becomes free after breaking an oath on the ruling of transitioning to a higher expiation option?

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It is debatable whether a slave who becomes free after breaking an oath may transition to a higher expiation option like a free person. One interpretation is that Ahmad's statement only means he is not obligated to switch. Another interpretation suggests a distinction between a freed slave and a free person, based on the notion that a free person could have chosen to borrow money for the higher expiation, while the slave, according to one narration, was only permitted the fasting option while enslaved.