What is the Shar'i ruling on the case of a man who married a woman, then her sister claimed her death, so the man married the daughter of her sister, and then the first wife appeared to be alive?

The jurists have agreed on the prohibition of combining a woman with her paternal aunt or her maternal aunt, based on the hadith (definition): "A woman should not be combined with her paternal aunt, nor a woman with her maternal aunt." The wisdom behind this is to preserve the ties of kinship and protect them from separation and animosity. The marriage to the second woman in this case is null and void, and does not necessitate divorce, dowry, or inheritance. So, if a man marries the daughter of his wife's sister, his marriage is void and he must separate from her immediately. However, he is permitted to marry her after the waiting period (iddah (definition)) of his first wife ends and she is divorced.

There is no sin upon the spouses for not intending the prohibition. If a pregnancy occurs, it is attributed to the husband because the spouses believed the marriage to be lawful.