مَرَرْتُ بِأَخِيكَ خَالِدٍ.
“I passed by your brother, Khālid.”
مَرَرْتُ: past verb with first-person subject.
بِأَخِيكَ: bi is a preposition; akhī is genitive with yāʾ, plus possessive kāf.
خَالِدٍ: genitive explanatory apposition with kasrah.
Across three cases, the role of clarifying identity remains the same, while the endings change.