مِّن أَلْفِ شَهْرٍ

مِّن أَلْفِ شَهْرٍ 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
  
than a thousand monthsمِّن أَلْفِ شَهْرٍ=شَهْرٍ+أَلْفِ+مِّن
 than thousand of monthsmonthsa thousand ofthan
Surah/Below is the only verse in the holy Quran containing the compoundمِّن أَلْفِ شَهْرٍ
Verse
97-3The night of Qadr is better than a thousand monthsلَيْلَةُ القَدْرِ خَيْرٌ مِّنْ أَلْفِ شَهْرٍ

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مِّنْ أَلْفِ شَهْرٍ occurrence

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