Tirmidhi

Yunus bin Ubaid, the freed slave of Muhammad bin Qasim, says that Muhammad bin Qasim sent me to Bara’ bin Azib (may Allah be pleased with them both) to ask him about the flag of the Messenger of Allah (peace and blessings of Allah be upon him). Bara’ said: “His flag was striped, square, and black.” © Imam Tirmidhi says:
1- This hadith is Hasan Gharib,
2- We know it only from the narration of Ibn Abi Zaidah,
3- In this chapter, hadiths have also been narrated from Ali, Harith bin Hissan, and Ibn Abbas (may Allah be pleased with them),
4- Abu Ya’qub Thaqafi’s name is Ishaq bin Ibrahim; from him, Ubaidullah bin Musa has also narrated.

'Abdullah bin Abbas (may Allah be pleased with them) says that the flag of the Messenger of Allah (peace and blessings of Allah be upon him) was black and the banner was white. © Imam Tirmidhi says:
This narration of Ibn Abbas with this chain is Hasan Gharib.