
From the life of Hazrat Ali (ra) bin Abi Talib
Hazrat Tha‘labah (ra) bin Abi Malik relates that Hazrat Saad (ra) bin Ubadah would be the flag-bearer for the Holy Prophet (sa) at the occasion of every battle; however, when the actual battle would commence, Hazrat Ali (ra) would take hold of the flag.
(Ali Ibn al-Athir, Usdul Ghabah fi Ma‘rifatis Sahabah, Vol. 4, [Beirut, Lebanon: Dar al-Fikr, 2003], p. 93)