Musannaf Ibn Abi Shaybah 34915 — What they said on wearing marks

Harithah bin Mudarrib al-Abdi (may Allah have mercy on him) said that Sayyiduna Ali (may Allah be pleased with him) said: On the day of the Battle of Badr, the mark of the Companions of the Messenger of Allah (peace and blessings be upon him) was white wool.