مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2401
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: I got up to pray with the Prophet (ﷺ) and I stood on his left. He reached back with his hand and took hold of my upper arm - or my arm - and made me stand on his right.
Musnad Ahmad 2413Its isnad is saheeh, al-Bukhari (727) and Muslim (763)]