Abu Dawud Book 36, Hadith Number 5252.

Narated By AbuUsayd al-Ansari : AbuUsayd heard the Apostle of Allah (PBUH) say when he was coming out of the mosque, and men and women were mingled in the road: Draw back, for you must not walk in the middle of the road; keep to the sides of the road. Then women were keeping so close to the wall that their garments were rubbing against it.