Abu Dawud Book 35, Hadith Number 4681.

Narated By AbuDharr AbuHurayrah : The Apostle of Allah (PBUH) used to sit among his Companions. A stranger would come, but did recognise him (the Prophet) until he asked (about him). So we asked the Apostle of Allah (PBUH) to make a place where he might take his seat so that when a stranger came, he might recognise him. So we built a terrace of soil on which he would take his seat, and we would sit beside him. He then mentioned something similar to this Hadith saying: A man came, and he described his appearance. He saluted from the side of the assembly, saying: Peace be upon you, Muhammad. The Prophet (PBUH) then responded to him.