مَرَرْتُ بِنِسْوَةٍ أَرْبَعٍ
Translation: I passed by four women.
مَرَرْتُ: past verb with attached first-person subject. بِ: preposition.
نِسْوَةٍ: genitive noun governed by bi-, with kasra and tanwīn.
أَرْبَعٍ: numerical modifier of «نِسْوَةٍ», genitive with kasra and tanwīn; the book classifies this use as munṣarif.
Do not call it a diptote merely because its visible pattern resembles the verb pattern.