1. Ordinary nominative sound masculine plural: مُسْلِمُونَ.
2. The plural nūn is removed for iḍāfa.
3. A possessive yāʾ meets the wāw; the book identifies the underlying form as مُسْلِمُوْيَ.
4. Wāw → yāʾ, followed by assimilation and ḍamma → kasra, gives مُسْلِمِيَّ.
This is an instructional sequence based on the textbook rule, not another direct quotation.