Musnad Ahmad 1015:26

Abu Abd al-Rahman said: I found in my father’s book, in his own handwriting: We were told by al-Abbas ibn al-Fadl al-Waqifi—meaning the Ansari from the tribe of Waqif—from Qurrah ibn Khalid, we were told by Budayl, we were told by Shahr ibn Hawshab, from Abd al-Rahman ibn Ghanam, who said: Abu Malik al-Ash'ari said: "Shall I not tell you about the prayer of the Messenger of Allah, may Allah bless him and grant him peace?" He said: "And he would say the salutation to his right and to his left." Then he said: "This is the prayer of the Messenger of Allah, may Allah bless him and grant him peace," and he mentioned the hadith.