Musannaf Ibn Abi Shaybah 12148 — Reports on greeting the graves when

Abdullah bin Sa'd al-Jari said: Sayyiduna Abu Hurayrah (may Allah be pleased with him) said to me: "O Abdullah! When you pass by a grave whose occupant you knew, say: 'Al-salamu alaykum ashab al-qubur' (Peace be upon you, O people of the graves); and when you pass by a grave whose occupant you do not know, say: 'Al-salamu ala al-muslimin' (Peace be upon the Muslims)."