Abu Dawud
General Behavior
Book Number: 036 / Hadith Number: 5191
Narated By Ali ibn AbuTalib : AbuDawud said: Al-Hasan ibn Ali traced this tradition back to the Prophet (pbuh): When people are passing by, it is enough if one of them gives a salutation on their behalf, and that it is enough for those who are sitting if one of them replies.