What is the grammatical status of yadā in tabbat yadā abī lahab?

Supplementary Practice 23: Comparative Rhetorical Study of Sūrat al-Masad and al-Ikhlāṣ

• Accusative object by yāʾ and indefinite
• Dual predicate of kāna, accusative by alif
• Genitive subject because it follows a verb
• Dual subject, nominative by alif, in construct