Abu Dawud Book 36, Hadith Number 5186.

Narated By AbuHurayrah : Suhayl ibn AbuSalih said: I went out with my father to Syria. The people passed by the cloisters in which there were Christians and began to salute them. My father said: Do not give them salutation first, for AbuHurayrah reported the Apostle of Allah (PBUH) as saying: Do not salute them (Jews and Christians) first, and when you meet them on the road, force them to go to the narrowest part of it.