Muwatta Malik, Book 28, Hadith 1137 (In-Book)

Yahya related to me from Malik from Ibn Shihab from Urwa ibn az- Zubayr that Khawla ibn Hakim came to Umar ibn al-Khattab and said, ''Rabia ibn Umayya made a temporary marriage with a woman and she is pregnant by him.'' Umar ibn al-Khattab went out in dismay dragging his cloak, saying, "This temporary marriage, had I come across it, I would have ordered stoning and done away with it! "

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عُرْوَةَ بْنِ الزُّبَيْرِ، أَنَّ خَوْلَةَ بِنْتَ حَكِيمٍ، دَخَلَتْ عَلَى عُمَرَ بْنِ الْخَطَّابِ فَقَالَتْ إِنَّ رَبِيعَةَ بْنَ أُمَيَّةَ اسْتَمْتَعَ بِامْرَأَةٍ فَحَمَلَتْ مِنْهُ ‏.‏ فَخَرَجَ عُمَرُ بْنُ الْخَطَّابِ فَزِعًا يَجُرُّ رِدَاءَهُ فَقَالَ هَذِهِ الْمُتْعَةُ وَلَوْ كُنْتُ تَقَدَّمْتُ فِيهَا لَرَجَمْتُ ‏.‏

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also referenced under: Book 28, Hadith 42 (USC-MSA)