Sahih Bukhari Volume 4, Book 61, Hadith 3558

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.‏

Narrated By '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 Apostle whose face was glittering with happiness, for whenever Allah's Apostle 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."