Al-Awza'i was asked about a Harbi man who is the husband of two sisters, so he said: "If it were not for that hadith in which it is transmitted that the Prophet (peace and blessings be upon him) gave the husband a choice in such a case, I would have given the fatwa that the man should remain with the woman whom he married first."

Imam Shafi'i says: When a person becomes Muslim and his wives are real sisters, then that person may choose whichever one of the two he wishes, and his marriage with that woman will remain valid, while his marriage with the other woman will be annulled. In this regard, it will make no difference whether (before accepting Islam) he married both of them at the same time or one after the other.

Sayyiduna Sahl bin Sa’d Sa’idi (may Allah be pleased with him) narrates: An Ansari man came to the service of the Prophet (peace and blessings of Allah be upon him) and said:“O Messenger of Allah! What is your opinion about a person who finds someone with his wife? If he kills the woman, you people will kill him. What should such a person do with the woman?”So Allah Almighty revealed the command about them, which is mentioned in the Qur’an regarding those who perform li’an (mutual cursing). The Prophet (peace and blessings of Allah be upon him) said to him:“Allah Almighty has decided between you and your wife.”The narrator states: Both husband and wife performed li’an in the mosque, and I was also present there with the Prophet (peace and blessings of Allah be upon him). (The narrator says) After that, this method became established regarding such husband and wife that separation would be made between those who performed li’an. The narrator says: The woman was pregnant, and the man denied the pregnancy, so after that, the son of that woman would be called by his mother’s name. After that, this method became established that such a woman would inherit from her child, and that child would inherit from the woman, as she had appointed as the inheritance of the son.

Amr bin Shu'aib narrates from his father, who narrates from his grandfather: An Ansari from the tribe of Banu Zuraiq accused his wife of adultery. He came to the Prophet Muhammad (peace be upon him), and the Prophet (peace be upon him) sent him back four times. Then Allah revealed the verses regarding the command of li'an (mutual cursing). The Prophet (peace be upon him) said: "Where is the questioner? A great command has been revealed from Allah." Then the man insisted on performing li'an, and the woman also decided that she would remove the punishment from herself. The narrator says: Both of them performed li'an. (Later) the Prophet (peace be upon him) said: "If this woman gives birth to a child with a yellow complexion, broad nose, and a weak body, then the child will belong to the man who performed li'an. But if she gives birth to a black child with a strong body like an ash-colored camel, then the child will belong to the other man." (The narrator says) The woman gave birth to a black child, who was like an ash-colored (i.e., dark-colored) camel. Then the Prophet (peace be upon him) called the child and handed him over to the relatives of his mother. He said: "If there had not already been an oath (i.e., li'an) regarding this, my decision would have been different." The wording of both (narrators) is the same.

Sayyiduna Sahl bin Sa’d Sa’idi (may Allah be pleased with him) narrates: I was present before the Prophet (peace and blessings be upon him) during the incident of li’an (mutual cursing) between a husband and wife. That man pronounced three divorces upon the woman in the presence of the Prophet (peace and blessings be upon him), and the Prophet (peace and blessings be upon him) validated them. Whatever is done in the presence of the Prophet (peace and blessings be upon him) becomes Sunnah, as long as the Prophet (peace and blessings be upon him) does not object to it. After this, the established Sunnah among those who performed li’an was that separation would be made between the husband and wife, and then they could never be together again.

Sayyiduna Sahl bin Sa’d Sa’idi (may Allah be pleased with him) narrates: ‘Uwaymir ‘Ajlani said to a member of his tribe:“You should ask the Prophet (peace and blessings of Allah be upon him) about a person who finds another man with his wife.”After that, he narrated the incident of those who performed li’an, in which these words are mentioned: Both of them performed li’an, so the Prophet (peace and blessings of Allah be upon him) separated them and said:“These two can never be together.”

Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates this statement of the Noble Prophet (peace and blessings be upon him): "When those who have invoked li'an (mutual cursing, i.e., the husband and wife) separate from each other, then they can never be together again."

Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: (What he said is mentioned in the next narration) Both Sayyiduna Ali (may Allah be pleased with him) and Sayyiduna Ibn Mas'ud (may Allah be pleased with him) say: "The established Sunnah regarding those who perform li'an is that the two can never be together again."

Sayyiduna Ali (may Allah be pleased with him) and Sayyiduna Ibn Mas'ud (may Allah be pleased with him), both said: "This is the established Sunnah that those who perform li'an can never be together again."

Sayyiduna Abdullah bin Ja'far (may Allah be pleased with him) narrates: I was present with the Prophet (peace and blessings of Allah be upon him) when he made 'Uwaymir 'Ajlani and his wife perform li'an. When the Prophet (peace and blessings of Allah be upon him) returned from Tabuk, 'Uwaymir denied the pregnancy in that woman's womb (being his child) and said: "This is the child of Ibn Sahma'." So the Prophet (peace and blessings of Allah be upon him) said: "Bring your wife, the command of the Qur'an has been revealed regarding both of you." The Prophet (peace and blessings of Allah be upon him) made both of them perform li'an regarding that pregnancy near the pulpit after the 'Asr prayer.