وَالْبَدَلُ إِنْ كَانَ نَكِرَةً مِنْ مَعْرِفَةٍ، يَجِبُ نَعْتُهُ، كَقَوْلِهِ تَعَالَى: ﴿بِالنَّاصِيَةِ نَاصِيَةٍ كَاذِبَةٍ﴾.
Translation: If the badal is indefinite while the antecedent is definite, the text requires it to be described by an adjective; as in the Qur’anic phrase: “by the forelock—a lying forelock.”
The source cites an excerpt from Qurʾān 96:15–16, not the complete verses. Al-nāṣiyah is definite, nāṣiyatin is the indefinite badal, and kādhibatin its adjective.