Sayyiduna Sahl bin Sa'd al-Sa'idi (may Allah be pleased with him) says regarding the li'an (mutual imprecation) of Uwaymir al-Ajlani that when the two of them had finished their li'an, Uwaymir said: If I keep her in my marriage, it will be as if I lied about her. So he gave her three divorces before the Messenger of Allah (peace and blessings be upon him) ordered him. It is stated in the book that Uwaymir gave three divorces in the presence of the Prophet (peace and blessings be upon him); had giving that been unlawful, he (peace and blessings be upon him) would have forbidden him. He says: If you must give divorce, then by giving three divorces together you will be a sinner, so do it this way.
The Shaykh said: In the narration of Ibn Umar (may Allah be pleased with them both) it is stated that the Prophet (peace and blessings be upon him) said about the two who made li'an: "Your reckoning is with Allah; one of you is a liar. You now have no authority over her." This is not in the narration of Sahl bin Sa'd (may Allah be pleased with him), and the three divorces are not in the narration of Ibn Umar (may Allah be pleased with them both). Imam al-Shafi'i (may Allah have mercy on him) took evidence from the hadith of Fatimah bint Qays (may Allah be pleased with her) that Abu Amr bin Hafs gave her three divorces, and no report has reached us that he (peace and blessings be upon him) forbade that.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 14935