Muwatta Malik, Book 19, Hadith 707 (In-Book)

Ziyad related to me from Malik that he had heard that Said ibn al-Musayyab used to say, "Whoever is present at isha on Laylat al-Qadr has taken his portion from it."

وَحَدَّثَنِي زِيَادٌ، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ سَعِيدَ بْنَ الْمُسَيَّبِ، كَانَ يَقُولُ مَنْ شَهِدَ الْعِشَاءَ مِنْ لَيْلَةِ الْقَدْرِ فَقَدْ أَخَذَ بِحَظِّهِ مِنْهَا ‏.‏

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also referenced under: Book 19, Hadith 17 (USC-MSA)