بِالنَّاصِيَةِ نَاصِيَةٍ كَاذِبَةٍ — By the forelock—a lying forelock.
بِـ: preposition.
النَّاصِيَةِ: genitive definite antecedent.
نَاصِيَةٍ: genitive indefinite badal with tanwīn.
كَاذِبَةٍ: genitive adjective of nāṣiyatin; it is not another badal.
The three share genitive case but have three distinct functions: antecedent, badal and adjective.