Muwatta Malik, Book 7, Hadith 260 (In-Book)

Yahya related to me from Malik that he had heard that Said ibn al-Musayyab used to say, "Sleep is disapproved of before isha and conversation after it."

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ سَعِيدَ بْنَ الْمُسَيَّبِ، كَانَ يَقُولُ يُكْرَهُ النَّوْمُ قَبْلَ الْعِشَاءِ وَالْحَدِيثُ بَعْدَهَا ‏.‏

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also referenced under: Book 7, Hadith 6 (USC-MSA)