«نَزَالِ»: final kasra is part of the fixed form, not proof of genitive case.
«مَرَرْتُ بِزَيْدٍ»: Zayd is genitive because it follows the preposition «بِ».
Identify the grammatical cause of an ending before labeling it.
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Fixed Kasra versus Genitive Kasra
Asmāʾ al-Afʿāl — Definition, Uses and Parsing
«نَزَالِ»: final kasra is part of the fixed form, not proof of genitive case.
«مَرَرْتُ بِزَيْدٍ»: Zayd is genitive because it follows the preposition «بِ».
Identify the grammatical cause of an ending before labeling it.