وَعَنْ كَعْبِ بْنِ مَالِكٍ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا سُرَّ اسْتَنَارَ وَجْهُهُ حَتَّى كَأَنَّ وَجْهَهُ قِطْعَةُ قَمَرٍ وَكُنَّا نَعْرِفُ ذَلِكَ. مُتَّفَقٌ عَلَيْهِ

Ka'b b. Malik said

When God's messenger was pleased his face lit up so that it looked like a bit of a moon, and we were familiar with that. (Bukhari and Muslim.)