Reference: Fataawa Ramadhaan – Volume 2, Page 514, Fatwa No.477
Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-`Ilmiyyah wal-Iftaa. – Fatwa No.6364
Question: Does going out during the day in Ramadhaan to attend to one’s needs and then being struck by the immodestly dressed women [who uncover those parts of the body which are prohibited to uncover] invalidate the fast or not?
Response: [No] it does not invalidate the fast, [however] he must lower his gaze to the best of his ability.
And with Allaah lies all the success, and may Allaah send prayers and salutations upon our Prophet Muhammad (sal-Allaahu `alayhi wa sallam) and his family and his companions.