Narrated Al-Bara' ibn Azib: Yunus ibn Ubayd, client of Muhammad ibn al-Qasim, said that Muhammad ibn al-Qasim sent to al-Bara' ibn Azib to ask him about the standard of the Messenger of Allah (ﷺ). He said: It was black and square, being made of a woollen rug

English translation · Sunan Abu Dawud