Bukhari

Explanation:
After returning from the migration to Abyssinia (Hijrah to Habashah), Abu Musa al-Ash‘ari radi Allahu anhu stayed at Baqi‘ Bathan. Baqi‘ refers to any place where there are various kinds of trees, etc. Bathan is the name of a valley near Madinah.

Imam Suyuti rahimahullah states that in previous nations (umam sabiqah), there was no ‘Isha prayer; therefore, the Prophet sallallahu alayhi wa sallam gave this glad tidings to his ummah, upon hearing which the noble Companions radi Allahu anhum were extremely pleased. It could also mean that in the other mosques of Madinah Sharif, people had already finished the ‘Isha prayer, but the worshippers in the Prophet’s Mosque (Masjid Nabawi) were still sitting in anticipation, and thus they attained this virtue. In any case, delaying the ‘Isha prayer is desirable. In one hadith, the Prophet sallallahu alayhi wa sallam said that if it were not difficult for my ummah, I would have performed the ‘Isha prayer after a third of the night had passed.

Hadith Commentary:
(1)
Multiple incidents regarding the ‘Isha prayer in the Prophet’s Mosque occurred at different times:
The incident narrated by Aisha (radi Allahu anha) took place at the beginning of Islam, as clarified in the previous hadith.
A considerable time after that, the incident involving Abu Musa al-Ash‘ari (radi Allahu anhu) and his companions occurred, because they had set out from Yemen to visit the Messenger of Allah (sallallahu alayhi wa sallam), but during their sea journey, a strong wind drove them to Abyssinia.
There, they stayed for seven years with Ja‘far al-Tayyar (radi Allahu anhu), then, in his company, they reached Madinah al-Munawwarah and camped in the valley of Bathan.
From there, some individuals would take turns each night at the time of ‘Isha to present themselves in the service of the Messenger of Allah (sallallahu alayhi wa sallam).
The aforementioned incident is from that period.
(Sahih al-Bukhari, al-Maghazi, Hadith: 4230)
After that, a similar incident occurred which was narrated by Ibn ‘Abbas (radi Allahu anhu).
Ibn ‘Abbas (radi Allahu anhu) arrived in Madinah Tayyibah in the eighth year of Hijrah.
It is evident that his eyewitness account would have occurred after the incident of Abu Musa al-Ash‘ari (radi Allahu anhu).
(Sahih al-Bukhari, Mawaqit al-Salat, Hadith: 571)
From these incidents, it is understood that the delay in the ‘Isha prayer used to occur in the Prophet’s Mosque itself, because the noble Companions (radi Allahu anhum) would come from various regions to the service of the Messenger of Allah (sallallahu alayhi wa sallam) to acquire religious knowledge.
Due to the constant engagement of the Messenger of Allah (sallallahu alayhi wa sallam) and his continuous arrangement for teaching and training day and night, the ‘Isha prayer would be delayed.
It is clear that such a delay would not be necessary in any mosque other than the Prophet’s Mosque.
And Allah knows best.

(2)
From some narrations, it is understood that this unusual delay regarding the ‘Isha prayer was due to the arrangement of a military expedition.
In any case, when the Prophet (sallallahu alayhi wa sallam) led the ‘Isha prayer after midnight, he gave glad tidings to those present that this was a special favor from Allah Ta‘ala, that at this time, no one else is praying except you; that is, your waiting was for a specific and distinctive prayer of Islam, so this is not devoid of reward, rather, there is a great reward in it for you.
Abu Musa al-Ash‘ari (radi Allahu anhu) says that after hearing the words of the Messenger of Allah (sallallahu alayhi wa sallam), we returned with such happiness the like of which cannot be described, because the Messenger of Allah (sallallahu alayhi wa sallam) had given us glad tidings for the act of the ‘Isha prayer and for waiting for it.