Uqbah bin Mughira narrates from his grandfather's father, Makharraq, who says: On the day of the Battle of Jamal, I met Sayyiduna Ammar (may Allah be pleased with him) while he was urinating in a horn. I said: I want to fight alongside you so that I may be with you, but he said: Fight while remaining under your own tribe's banner, because the Messenger of Allah (peace and blessings be upon him) liked that a man should fight under his own tribe's banner.
Hadith Referenceالفتح الربانی / كتاب الجهاد / 4970