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.
Reference: Sunan Abi Dawud 2591 In-book : Book 15, Hadith 115 English translation : Book 14, Hadith 2585
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