مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3463
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Miqsam said: I only know it from Ibn ‘Abbas (رضي الله عنه), that the banner of the Prophet (ﷺ) was with 'Ali bin Abi Talib, and the banner of the Ansar was with Sa'd bin 'Ubadah, and when the fighting intensified, The Messenger of Allah (ﷺ) would be under the banner of the Ansar.
Musnad Ahmad 3486lts isnad is da'eef]