Musnad Ahmad 25:932

Ibrahim ibn Ishaq narrated to us, al-Fadl ibn Musa narrated to us, from Abdullah ibn Sa'id ibn Abi Hind, he said: Thawr narrated to me, from Ikrimah, from Ibn Abbas, he 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, and he would not twist his neck."