Musnad Abu Ya'la al-Mawsili 6:113

Abu Khaythama narrated to us, Abd al-Rahman ibn Mahdi and Abu Sa'id, the freed slave of Banu Hashim, narrated to us, from Abdullah ibn Ja'far, from Isma'il ibn Muhammad ibn Sa'd, from Amir ibn Sa'd, from his father, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to perform the taslim to his right until his cheek appeared, and to his left until his cheek appeared.