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

This Hadith is Hasan Gharib from this route, as a narration of Ibn 'Abbas.
Jami` at-Tirmidhi Book 23, Hadith 12
← Previous Hadith 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.'"

There are narrations on this topic from 'Ali, Al-Harith bin Hassan, and Ibn 'Abbas.

This Hadith is Hasan Gharib, we don know know of it except from the report of Ibn Abi Za'idah. And Abu Ya'qub Ath-Thaqafi's name is Ishaq bin Ibrahim. 'Ubaidullah bin Musa also reports from him.

Jami` at-Tirmidhi Book 23, Hadith 11 Next Hadith → From one who heard the Prophet (ﷺ) saying: "If you suffer a surprise attack from the enemy then say: 'Ha Min, they will not be victorious.'"

There is something on this topic from Salamah bin Al-Akwa'. This is how some of them reported it from Abu Ishaq, the same as the narration of Ath-Thawri. And it has been reported from him, from Al-Muhallab bin Abi Sufrah from the Prophet (ﷺ) in Mursal form.

Jami` at-Tirmidhi Book 23, Hadith 13