وَيَخْتَصُّ بِجَمْعِ الْمُذَكَّرِ السَّالِمِ مُضَافًا إِلَى يَاءِ الْمُتَكَلِّمِ.
Translation: This rule is restricted to a sound masculine plural placed in an iḍāfa construction with the first-person possessive yāʾ.
Both conditions apply: a sound masculine plural and a following first-person possessive pronoun as muḍāf ilayh. The ordinary مُسْلِمُونَ / مُسْلِمِينَ pattern was studied earlier.