مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3335
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that al-A'mash said: I asked Ibraheem about a man praying with the imam. He said: He should stand to his left. I said: Sumai’ az-Zayyat told me: I heard Ibn ‘Abbas (رضي الله عنه) narrate that the Prophet (ﷺ) made him stand on his right, and he accepted that.
Musnad Ahmad 3359Its isnad is saheeh]