Bukhari

Hadith Commentary:
It is understood that in jihad, the prophetic standard was carried.
And the one who would carry it was Qays ibn Sa'd al-Ansari radi Allahu anhu.
In the Battle of Khaybar, the one who carried this banner was Ali radi Allahu anhu,
as will be mentioned further ahead.

Hadith Commentary:
➊
(Loa’, raya, and ‘alam)
All three are names for a flag.
In reality, the commander of the army would hold the flag.
It would be waved above his head.
Imam Bukhari rahimahullah’s purpose is to show that keeping flags in battles is permissible.
And sometimes it is in the hand of the leader, and sometimes in the hand of his deputy; it is protected.
Its being lowered is as if it is a sign of Islam being lowered.
➋
Although this hadith is mawquf (stopped at the Companion), the part for which evidence is sought is, in effect, considered marfu‘ (attributed to the Prophet sallallahu alayhi wa sallam), because Qays ibn Sa‘d radi Allahu anhu holding the flag would certainly have been by the command and permission of the Messenger of Allah sallallahu alayhi wa sallam.
And here, the intent is also to establish the permissibility of the flag.