Is *Istibra'* (purgation period) required for a female slave (*amah*) whom the master had relations with, if he frees her afterwards?

Primary text

If a master has relations with his female slave and performs *Istibra'* upon her, and then frees her, she is not required to undergo another *Istibra'* period. This is because freeing her removes her status as permissible sexual property (*firash*), which was established by the initial *Istibra'*.