رَأَيْتُ مُسْلِمَاتٍ.
Translation: I saw Muslim women.
Grammatical analysis
رَأَيْتُ: past-tense verb; the final تُ is its subject pronoun.
مُسْلِمَاتٍ: direct object, hence accusative.
Accusative sign: kasra, because this is a sound feminine plural.
Although the form ends in kasra, it is accusative, not genitive, in this sentence.