the freed salve of Muhammad bin Al-Qasim said: "Muhammad bin Al-Qasim sent me to Al-Bara' bin 'Azib to ask him about the flag of the Messenger of Allah ﷺ. He said: 'It was a black square of Namirah.'"  

عَنْ رَايَةِ رَسُولِ اللَّهِ ﷺ فَقَالَ كَانَتْ سَوْدَاءَ مُرَبَّعَةً مِنْ نَمِرَةٍ  

"The flag of the Messenger of Allah ﷺ was black, and his standard was white."  

كَانَتْ رَايَةُ رَسُولِ اللَّهِ ﷺ سَوْدَاءَ وَلِوَاؤُهُ أَبْيَضَ