Musannaf Ibn Abi Shaybah 12147 — Reports on greeting the graves when

Amir bin Sa'd narrates from his father that when he returned from his estate (village), he passed by the graves of the martyrs and said: 'Al-salamu alaykum wa inna bikum la-lahiqun' (Peace be upon you, and we will surely join you). Then he said to his companions: "Why did you not greet the martyrs, so that they would reply to you?"