يَا عَبْدَ اللهِ!
Translation: O ʿAbd Allāh!
يَا: indeclinable particle of address.
عَبْدَ: accusative vocative in an iḍāfa construction; the first term.
اللهِ: genitive second term of iḍāfa.
Because “ʿabd” is muḍāf, it takes an overt accusative fatḥa, not the fixed ḍamma of a single proper-name vocative.
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Al-Munādā: Vocative Types and Rules
يَا عَبْدَ اللهِ!
Translation: O ʿAbd Allāh!
يَا: indeclinable particle of address.
عَبْدَ: accusative vocative in an iḍāfa construction; the first term.
اللهِ: genitive second term of iḍāfa.
Because “ʿabd” is muḍāf, it takes an overt accusative fatḥa, not the fixed ḍamma of a single proper-name vocative.