Authentic Supplication Number 221.

It is reported that the Prophet said: "It would suffice a group that is passing by, that one of them says 'As-Salam, and it would suffice those sitting down, that one of them replies."

Reporters.
Reported by 'Abu Dawood. Al-Albani said it was comely, that Ahmed, and al-Bayhaqi also reported it, and that there was some weakness in it, but that it had testimonials that strengthened it. Al-Albani included this hadeeth in The Authentic of Good Sayings as #158.