مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2771
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas (رضي الله عنه) said: The Messenger of Allah (ﷺ) used to turn right and left in his prayer without twisting his neck.
Musnad Ahmad 2791Its isnad is saheeh]