مِّن خَوْفٍ

مِّن خَوْفٍ is a phrase (شِبْهُ الجُمْلَةِ), a compound consisting of a particle of pulling down (preposition) and a genitive noun

PhraseParticle/NounNoun Particle 
شِبْهُ الجُمْلَةِجَارٌ وَمَجْرُوْرٌاسْمٌ مَجْرُوْرٌحَرْفُ جَرٍّ
PhraseCompoundGenitive NounParticle of pulling down
  
from fearمِّن خَوْفٍ=خَوْفٍ+مِّن
from fearfearfrom
Surah/Below is the only verse in the holy Quran containing the compoundمِّن خَوْفٍ
Verse
  
106-4Who fed them against hunger and secured them against fearالَّذِي أَطْعَمَهُم مِّن جُوْعٍ وَّآمَنَهُم مِّن خَوْفٍ