باب ما جاء في خلق رسول الله صلى الله عليه وسلم
1  
The Noble Features Of Rasoolullah
Ash-Shama'il Al-Muhammadiyah 15
Ibn 'Abbas said:
Allah’s Messenger (Allah bless him and give him peace) had a gap between the medial pair of teeth. When he spoke, it seemed as if light were emerging from between his middle teeth."
حَدَّثَنَا عَبْدُ اللهِ بْنُ عَبْدِ الرَّحْمَنِ، قَالَ‏:‏ حَدَّثَنَا إِبْرَاهِيمُ بْنُ الْمُنْذِرِ الْحِزَامِيُّ، قَالَ‏:‏ حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ أَبِي ثَابِتٍ الزُّهْرِيُّ، قَالَ‏:‏ حَدَّثَنِي إِسْمَاعِيلُ بْنُ إِبْرَاهِيمَ ابْنُ أَخِي مُوسَى بْنِ عُقْبَةَ، عَنْ مُوسَى بْنِ عُقْبَةَ، عَنْ كُرَيْبٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ‏:‏ كَانَ رَسُولُ اللهِ صلى الله عليه وسلم أَفْلَجَ الثَّنِيَّتَيْنِ، إِذَا تَكَلَّمَ رُئِيَ كَالنُّورِ يَخْرُجُ مِنْ بَيْنِ ثَنَايَاهُ‏.‏
Grade: Da'if jiddan (Zubair Alizai)  ضعيف جدا   (Zubair Alizai) حكم   :
Reference : Ash-Shama'il Al-Muhammadiyah 15
In-book reference : Book 1, Hadith 14
Explanation
comments
According to the Ulama, it is a well known fact that it was something similar to nur which emitted from his teeth. The opinions of Allaamah Munaawi is that it was something sensory, and not a similarity, which emitted miraculously from between the teeth of Rasulullah (Sallallahu alaihe wasallam).

Everything of his noble features was perfect and beautiful. In the manner that is real and intrinsic beauty had reached its last stage, in the same manner his zaahiri (apparent) beauty had also reached its fullest and proper stage. Allahumma sali 'alaa Sayyidina Muhammadiw wa 'alaa aalihi biqadri husnihi wa jamaalihi.
Hadith Text
Reference