Musnad Abu Ya'la al-Mawsili 110:266

Zuhayr narrated to us, Ibrahim Abu Ishaq narrated to us, al-Fadl ibn Musa narrated to me, from Abdullah ibn Sa’id ibn Abi Hind, Thawr narrated to me, from Ikrimah, from Ibn Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to turn in his prayer to the right and to the left, but he would not twist his neck.