What is the grammatical role of ṣudūr in fī ṣudūr al-nās?

Supplementary Practice 24 — Comparative Rhetoric of Sūrat al-Falaq and Sūrat al-Nās

• Genitive after fī and annexed to al-nās
• Nominative subject of yuwaswisu
• Accusative object of qul
• Accusative subject of inna