فِي تَضْلِيْلٍ

فِي تَضْلِيْلٍ is a phrase (شِبْهُ الجُمْلَةِ) 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
  
into loss (astray)فِي تَضْلِيْلٍ=تَضْلِيْلٍ+فِي 
into losslossinto
Surah/Below is the only verse in the holy Quran containing the genitive particle and genitive noun compoundفِي تَضْلِيْلٍ
Verse
105-2Did He not make their plan go astray?أَلَم يَجْعَلْ كَيْدَهُم فِي تَضْلِيْلٍ