Musnad Abu Ya'la al-Mawsili 151:85

And with his chain of narration from Abdullah ibn Mas’ud, he said: It is as if I am looking at the whiteness of the cheek of the Messenger of Allah, may Allah bless him and grant him peace, to his right: "Peace be upon you and the mercy of Allah and His blessings." "Peace be upon you and the mercy of Allah," to his left.