Muwatta Malik, Book 28, Hadith 39 (USC-MSA)

Yahya related to me from Malik from Ibn Shihab that Said ibn al- Musayyab said, "The muhsanat among women are those who have husbands." That referred to the fact that Allah has made fornication haram.

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّهُ قَالَ الْمُحْصَنَاتُ مِنَ النِّسَاءِ هُنَّ أُولاَتُ الأَزْوَاجِ وَيَرْجِعُ ذَلِكَ إِلَى أَنَّ اللَّهَ حَرَّمَ الزِّنَا ‏.‏

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also referenced under: Book 28, Hadith 1134 (In-Book)