Ibn 'Abbas said, "The Messenger of Allah, may Allah bless him and grant him peace, passed by some graves at Madina and turned his face towards them and said, "Peace be upon you, O people of the graves! May Allah forgive us and you. You preceded us and we are following afterwards."

Riyadh-as-Saliheen by Imam Al-Nawawi, volume 4, hadith number 584 - Sunni Hadith