What is the ruling on intercourse resulting from a marriage contract universally agreed upon as void?

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When intercourse occurs under a marriage contract universally agreed upon as void—such as marrying a fifth wife, a married woman, a woman observing 'iddah (waiting period), or a woman divorced three times—and the man engages in it while knowing the prohibition, the act constitutes Zina (fornication/adultery) requiring the prescribed legal punishment (Hadd) to be applied before the invalid contract. This is the position held by Al-Shafi'i. The evidence for this ruling is derived from reports concerning Companions. It is narrated on the authority of Ubayd ibn Nadlah that a woman who married while observing her 'iddah was brought before Umar ibn Al-Khattab. When he learned they were unaware of the prohibition, he stated that had they known, he would have ordered their stoning. He then had the woman flogged with whips and separated them. Furthermore, it is reported that when a woman married another man while still having a husband whom she concealed, Ali, peace be upon him, ordered her to be stoned, and the second husband was flogged one hundred lashes.