بِالنَّاصِيَةِ

بِالنَّاصِيَةِ is a phrase (شِبْهُ الجُمْلَةِ) consisting of a particle of pulling down (a preposition) and a genitive noun

PhraseParticle / NounNoun Particle
شِبْهُ الجُمْلَةِجَارٌ وَمَجْرُوْرٌاسْمٌ مَجْرُوْرٌحَرْفُ جَرٍّ
PhraseCompoundGenitive NounParticle of pulling down/Preposition
  
by the forelockبِالنَّاصِيَةِ=النَّاصِيَةِ+بِ
by the forelockthe forelockby
Surah/Below is the only verse in the holy Quran containing the compoundبِالنَّاصِيَةِ
Verse
96-15Nay! if he ceases not, We will surely catch him by the forelockكَلَّا لَئِنْ لَّمْ يَنْتَهِ لَنَسْفَعًا بِالنَّاصِيَةِ