Prayer (Kitab Al-Salat): Details of Commencing Prayer
Dawud :: Book 3 : Hadith 992
Narrated Wa'il ibn Hujr:
I offered prayer along with the Prophet (peace_be_upon_him). He would give the salutation to his right side (saying): Peace be upon you and mercy of Allah; and to his left side (saying): Peace be upon you and mercy of Allah.