It is narrated from Abu Hurairah (may Allah be pleased with him) that Sa'd (bin 'Ubadah, may Allah be pleased with him) said: "O Messenger of Allah (ﷺ)! If I find a man with my wife, should I wait until I bring four witnesses?" The Messenger of Allah (ﷺ) said: "Yes."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1699
It is narrated from Abu Huraira (may Allah be pleased with him) that Sa'd (may Allah be pleased with him) asked: "O Messenger of Allah (ﷺ)! If I find a man with my wife, should I wait until I bring four witnesses?" The Messenger of Allah (ﷺ) replied: "Yes."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1700
It is narrated from Ibn Musayyib that Ali bin Abi Talib (may Allah be pleased with him) was asked about a man who found another man with his wife and killed him, or killed his wife, so he said: "If he does not bring four witnesses, then he should be prepared to be killed himself."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1701
It is narrated from Sa'id bin al-Musayyib that in Syria, a man found another man with his wife and killed him, or he killed the woman. So (the governor of Syria) Mu'awiyah, may Allah be pleased with him, wrote to Abu Musa al-Ash'ari, may Allah be pleased with him, that you should ask this matter for them from Ali, may Allah be pleased with him. He asked Ali, may Allah be pleased with him, and he said: "This incident did not happen in the land of Iraq. I adjure you to speak the truth." Then he told the reality, so Ali, may Allah be pleased with him, said: "I am Abu al-Hasan. If he does not bring four witnesses, then he should be content with being killed."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1702
Hadith Takhrijاسناده صحیح اخرجه البيهقي : 8 / 230 ، 10 / 147 - وفى المعرفة السنن والآثار له (5277) ۔ وعبد الرزاق (17915) ، (17916) وابن ابى شيبة (27879) - ومالك فى الموطا الأقضية، باب القضاء فيمن وجد مع امرأته رجلا۔