Apply the longer-maqsur rule to the new noun مُسْتَشْفَى. Which nominative dual follows?

Dual and Plural of Mamdud and Maqsur Nouns

• مُسْتَشْفَاءَانِ
• مُسْتَشْفَيَانِ
• مُسْتَشْفَوَانِ
• مُسْتَشْفَوْنَ