مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2473
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: The Prophet (ﷺ) used to turn to the right and to the left, but he did not twist his neck all the way to the back.
Musnad Ahmad 2485Its isnad is saheeh]