Mishkat al-Masabih 29 Excellent Qualities and Description of the Prophet كتاب الفضائل والشمائل 57

عَنِ ابْنِ عَبَّاسٍ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَفْلَجَ الثَّنِيَّتَيْنِ إِذَا تَكَلَّمَ رُئِيَ كَالنُّورِ يَخْرُجُ مِنْ بَيْنِ ثَنَايَاهُ. رَوَاهُ الدَّارمِيّ

Ibn `Abbas said: God’s messenger had spaces between his front teeth, and when he talked something like light seemed to come out between his front teeth. Darimi transmitted it.