لِّ

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – لِّ is a particle

لِّ is a preposition as in لِلَّهِ denoting possession, meaning ‘to’, ‘for’, ‘unto’, ‘on account of’, ‘belonging to’

لِّ is the same as the preposition لِلforحَرْفٌحَرْفُ جَرٍّ
it takes a shaddah due to the indefinite noun preceding it in the sentenceRootbelongs toParticleParticle of pulling down لِّ
Surah/Below are verses in the holy Quran containing the prepositionلِّ
Verse
  
104-1Woe to every slanderer and backbiterوَيْلٌ لِّكُلِّ هُمَزَةٍ لُّمَزَةٍ
107-4So, woe to the worshippersفَوَيْلٌ لِّلْمُصَلِّيْنَ