What is the ruling regarding the punishment for slander when the accused person is later proven to have committed the act he was falsely accused of?

Primary text

The evidence supports that the punishment for slander is obligatory even if the accused is later found to have actually committed the act. This is supported by the report that a man confessed to the Prophet (peace be upon him) to having committed fornication four times; he was flogged one hundred times. When the woman denied it, he was flogged with the punishment for false accusation (hadd al-firya) eighty times. Furthermore, the possibility of error, such as in the case of one who married his mother, does not negate the punishment for slander.