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كتاب المناقب
61  
Virtues and Merits of the Prophet (pbuh) and his Companions
(23)
Chapter: The description of the Prophet (saws)
(23)
باب صِفَةِ النَّبِيِّ صلى الله عليه وسلم
Sahih al-Bukhari 3556

Narrated `Abdullah bin Ka`b:

I heard Ka`b bin Malik talking after his failure to join (the Ghazwa of) Tabuk. He said, "When I greeted Allah's Messenger (ﷺ) whose face was glittering with happiness, for whenever Allah's Messenger (ﷺ) was happy, his face used to glitter, as if it was a piece of the moon, and we used to recognize it (i.e. his happiness) from his face."

حَدَّثَنَا يَحْيَى بْنُ بُكَيْرٍ، حَدَّثَنَا اللَّيْثُ، عَنْ عُقَيْلٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ عَبْدِ اللَّهِ بْنِ كَعْبٍ، أَنَّ عَبْدَ اللَّهِ بْنَ كَعْبٍ، قَالَ سَمِعْتُ كَعْبَ بْنَ مَالِكٍ، يُحَدِّثُ حِينَ تَخَلَّفَ عَنْ تَبُوكَ، قَالَ فَلَمَّا سَلَّمْتُ عَلَى رَسُولِ اللَّهِ صلى الله عليه وسلم وَهْوَ يَبْرُقُ وَجْهُهُ مِنَ السُّرُورِ، وَكَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا سُرَّ اسْتَنَارَ وَجْهُهُ، حَتَّى كَأَنَّهُ قِطْعَةُ قَمَرٍ، وَكُنَّا نَعْرِفُ ذَلِكَ مِنْهُ‏.‏
Reference : Sahih al-Bukhari 3556
In-book reference : Book 61, Hadith 65
USC-MSA web (English) reference : Vol. 4, Book 56, Hadith 756
  (deprecated numbering scheme)