Abu al-Zubair narrated that a case of marriage was brought to Umar (may Allah be pleased with him) in which there was only one man and one woman as witnesses. So he (may Allah be pleased with him) said: "This is a secret marriage, and I do not consider it permissible, and if I had declared this earlier, I would have stoned (the parties involved)."
Hadith Referenceمسند الإمام الشافعي / كتاب النكاح / 1144
Hadith Takhrijاسناده ضعيف لانقطاعه، فان ابا الزبير لم يسمع من عمر اخرجه البيهقي: 7 / 126 - وفي المعرفة السنن والآثار له (4103)۔