حَتَّى مَطْلَعِ الفَجْرِ

حَتَّى مَطْلَعِ الفَجْرِ is a phrase (شِبْهُ الجُمْلَةِ) consisting of a particle and a nominal compound

PhraseParticle / Noun / NounNounNounParticle
 شِبْهُ الجُمْلَةِجَارٌ وَمَجْرُوْرٌ وَهُوَ مُضَافٌ وَ مُضَافٌ إِلَيْهِمُضَافٌ إِلَيْهِاسْمٌ مَجْرُوْرٌ وَهُوَ مَضَافٌحَرْفُ جَرٍّ
PhraseCompoundpossessive nounGenitive noun + Noun possessedParticle of pulling down
  
until the emergence of dawnحَتَّى مَطْلَعِ الْفَجْرِ=الفَجْرِ+مَطْلَعِ+حَتَّى
 until the emergence of dawndawnthe emergence ofuntil
Surah/Below is the only verse in the holy Quran containing the compoundحَتَّى مَطْلَعِ الْفَجْرِ
Verse
97-5Peace it is until the emergence of Dawnسَلَامٌ هِيَ حَتَّى مَطْلَعِ الفَجْرِ