Muwatta Malik, Book 51, Hadith 16 (USC-MSA)

Yahya related to me from Malik that he had heard that Abdullah ibn Abbas said, "Equanimity, gentleness, and good behaviour are one twenty-fifth of prophecy."

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ عَنْ عَبْدِ اللَّهِ بْنِ عَبَّاسٍ، أَنَّهُ كَانَ يَقُولُ الْقَصْدُ وَالْتُّؤَدَةُ وَحُسْنُ السَّمْتِ جُزْءٌ مِنْ خَمْسَةٍ وَعِشْرِينَ جُزْءًا مِنَ النُّبُوَّةِ ‏.‏

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also referenced under: Book 51, Hadith 1749 (In-Book)