Hazrat Ibn Aun (may Allah have mercy on him) narrates that Hazrat Umair bin Ishaq (may Allah have mercy on him) said: On the day of the Battle of Badr, the Companions (may Allah be pleased with them) were told: Make some sign and mark for yourselves. Indeed, the angels have also put on a sign. He said: On that day, wool was used as a sign for the first time.