Bukhari

Hadith Commentary:
This does not contradict the narration in which nine expeditions are mentioned with the Prophet (sallallahu alayhi wa sallam).
Perhaps Salamah considered the journeys to Wadi al-Qura and the ‘Umrah of Compensation (Umrat al-Qada) as expeditions (jihad) as well, thus making them nine.
Qastallani said: This hadith is the fifteenth thulathi (three-narrator chain) hadith of Imam al-Bukhari.
Harithah is the name of the grandfather of Usamah (radi Allahu anhu).
(Wahidi)

Hadith Commentary:
The accounts of all these battles (ghazawat) have been mentioned at various places within this section (para).
The incident of Dhat al-Qird can be observed at the beginning of the section.
This was a battle (ghazwah) against those bandits who were driving away twenty milch she-camels belonging to the Messenger of Allah (sallallahu alayhi wa sallam).
This incident occurred a few days before the Battle of Khaybar (Ghazwah Khaybar).
Furthermore, the other battles whose names were forgotten refer to the Battle of the Conquest of Makkah (Ghazwah Fath Makkah), the Battle of Ta’if (Ghazwah Ta’if), and the Battle of Tabuk (Ghazwah Tabuk).
(Fath)

Hadith Commentary:
Yazid bin Abu Ubaid was the freed slave of Salamah bin Akwa’ radi Allahu anhu.

The details of the seven military expeditions (ghazawat) in which Salamah bin Akwa’ radi Allahu anhu participated alongside the Messenger of Allah sallallahu alayhi wa sallam are as follows:
The Expedition of Khaybar, the Expedition of Hudaybiyyah, the Expedition of Hunayn, the Expedition of Qard, the Expedition of the Conquest of Makkah, the Expedition of Ta’if, and the Expedition of Tabuk.
And this (Tabuk) was the last expedition of the Messenger of Allah sallallahu alayhi wa sallam.

In one narration, nine expeditions are mentioned.
It is possible that among them, one is the Expedition of Wadi al-Qura, which took place after Khaybar, and the other is ‘Umrat al-Qada, which may have been counted as an expedition.
(Fath al-Bari: 7/648. )

And among the expeditions (saraya) in which Abu Bakr radi Allahu anhu was appointed as commander, are the Expedition of Banu Fazarah and the Expedition of Banu Kilab. Similarly, in the ninth year of Hijrah, he was sent for Hajj, and this too was under the leadership of Abu Bakr radi Allahu anhu. Likewise, there is mention of another expedition under the leadership of Usamah radi Allahu anhu.
These are five expeditions; the remaining four can also be searched for.
(Fath al-Bari: 7/649. )

In these expeditions, the Messenger of Allah sallallahu alayhi wa sallam sometimes appointed elders like Abu Bakr radi Allahu anhu as commander of the army, and sometimes young men like Usamah radi Allahu anhu. However, no one ever entertained the thought regarding the matter of command as to whether the commander was young or old; rather, all participants submitted themselves before the noble command of the Messenger of Allah sallallahu alayhi wa sallam.

The Messenger of Allah sallallahu alayhi wa sallam said that even if an Abyssinian slave is appointed over you as commander, it is obligatory upon you to obey him.
(Sahih al-Bukhari, al-Ahkam, Hadith: 7142. )

Hadith Commentary:
The narrator's intent is that, in all the military expeditions (ghazawat), the Messenger of Allah (sallallahu alayhi wa sallam) sometimes appointed elders like Abu Bakr (radi Allahu anhu) as the commander of the army, and at other times appointed young men like Usamah (radi Allahu anhu). Yet, we never considered the age or status of the commander; rather, we bowed our heads in submission before the command of the Messenger (sallallahu alayhi wa sallam).
He (sallallahu alayhi wa sallam) repeatedly stated that even if an Abyssinian (Habashi) slave is appointed over you as commander, it is obligatory for you to obey him.