Imam al-Shafi'i (may Allah have mercy on him) said: "Since the Messenger of Allah (peace and blessings be upon him) made Sayyiduna Rukanah (may Allah be pleased with him) swear an oath in the matter of divorce, this indicates that the oath in divorce is just as it is in other matters."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / Q20727
Ibn Abi Mulaykah said: Ibn Abbas (may Allah be pleased with them both) wrote to me that the Prophet (peace and blessings be upon him) "placed the oath upon the defendant."
(b) This covers every defendant, except where evidence establishes otherwise.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20727
Nafi' narrates from Abdullah bin Umar (may Allah be pleased with them both): When a man hands over to his wife the authority over her matter, then the decision is whatever she decides, unless he disputes it with her, saying: I intended only one divorce. He swears to that, and the matter is returned to him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20728
Nafi' (may Allah have mercy on him) narrates from Sayyiduna Ibn Umar (may Allah be pleased with them both): When a woman claims that her husband divorced her and they dispute it, then he takes an oath by Allah that he did not do it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20729