مَرَرْتُ بِأَخِيكَ.
Translation: I passed by your brother.
مَرَرْتُ: past-tense verb with the subject pronoun تُ.
بِ: preposition.
أَخِي: genitive noun with yāʾ as the genitive case sign; also the first term of iḍāfa.
كَ: attached pronoun, second term of iḍāfa, in the genitive position.
Key point: The preposition بِ causes genitive case; the sign on this particular noun is yāʾ, not a kasra ending.
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Noun Case Classes: Type 4 — The Six Nouns
مَرَرْتُ بِأَخِيكَ.
Translation: I passed by your brother.
مَرَرْتُ: past-tense verb with the subject pronoun تُ.
بِ: preposition.
أَخِي: genitive noun with yāʾ as the genitive case sign; also the first term of iḍāfa.
كَ: attached pronoun, second term of iḍāfa, in the genitive position.
Key point: The preposition بِ causes genitive case; the sign on this particular noun is yāʾ, not a kasra ending.