Bukhari

Hadith Commentary:
This incident pertains to the expedition of Anmar. For those traveling there, the qiblah remains on the left side. The ruling includes riding camels and every animal.

Hadith Commentary:
It is permissible to perform voluntary (nafl) prayers while riding an animal, and it is sufficient to perform the bowing (ruku) and prostration (sujud) by means of gestures.
In one narration, it is mentioned that when beginning prayer on a camel, the Prophet (sallallahu alayhi wa sallam) would face the qiblah and pronounce the opening takbir.

Hadith Commentary:
1.
Imam Bukhari rahimahullah has mentioned this hadith to state an exceptional case regarding the obligation of facing the qiblah during prayer; that is, if one intends to perform a supererogatory (nafl) prayer, then facing the qiblah is not obligatory. However, it is mentioned in Sunan Abu Dawud that when the Prophet sallallahu alayhi wa sallam wished to perform a nafl prayer on his mount during travel, he would first turn the face of the mount towards the qiblah, then pronounce the opening takbir (takbir tahrimah) and begin the prayer. After that, he would not mind in whichever direction the mount turned. However, for obligatory (fard) prayers, he would dismount and perform the prayer facing the qiblah.
(Sunan Abu Dawud, Salat al-Safar, Hadith: 1225)

2.
Based on the principle of "necessities permit the prohibited" (al-darurat tubih al-mahzurat), if there is intense fear, then the condition of facing the qiblah for obligatory prayer is waived.
Similarly, if it rains during travel and there is no dry place available to pray, one may stop the mount, face it towards the qiblah, and perform the prayer. However, the common practice of praying while seated in trains and buses requires correction, because both facing the qiblah and standing (qiyam) are necessary in prayer.
Both of these are lost when praying in trains and buses.
The Islamic government should allocate a compartment in train carriages specifically for the performance of prayer, in which water and the direction of the qiblah are arranged.

Hadith Commentary:
Ibn Ishaq has mentioned that this expedition took place in the month of Safar, and Ibn Sa’d states that a man came from Halab and informed that Banu Anmar and Banu Tha’labah were gathering to fight the Muslims, so the Prophet (sallallahu alayhi wa sallam) set out on the 10th of Safar and reached their location at the site of Dhat al-Riqa’.
It has also been said that the expedition of Anmar occurred at the end of the expedition of Banu Mustaliq, on the 27th of Safar, because Abu al-Zubayr narrated from Jabir (radi Allahu anhu) that the Prophet (sallallahu alayhi wa sallam) was going for the expedition of Banu Mustaliq.
I presented myself in service and saw that he was praying on top of a camel.
This is also supported by the narration of Layth, in which it is mentioned that the Messenger of Allah (sallallahu alayhi wa sallam) performed the prayer of fear (salat al-khawf) in the expedition of Banu Anmar.
It is also possible that there were multiple incidents.
(Fath al-Bari)

Hadith Commentary:
➊
It is permissible to perform voluntary (nafl) prayers while riding an animal.
In this, facing the qiblah is not necessary, nor is it obligatory to place the forehead on the ground during prostration (sajdah); rather, bowing (ruku) and prostration can be performed by gesture.
However, Imam Bukhari rahimahullah did not mention this hadith here to discuss the jurisprudential ruling, but rather he presented it as evidence for the occurrence of the Expedition of Anmar.
➋
An objection has been raised regarding Imam Bukhari’s methodology, that the mention of this expedition should have come earlier, and that it is not appropriate to mention it in the context of the Expedition of Banu Mustaliq.
Perhaps Imam Bukhari’s position is that the Expedition of Anmar took place during the Expedition of Muraysi‘.
Accordingly, Abu Zubair narrated from Jabir radi Allahu anhu that when the Prophet sallallahu alayhi wa sallam was going for the Expedition of Banu Mustaliq, I came to him and he was praying on his camel. The narration of Layth also supports the fact that in the Expedition of Anmar, the Messenger of Allah sallallahu alayhi wa sallam performed the prayer of fear (salat al-khawf).
It is also possible that there were multiple incidents.
(Fath al-Bari: 7/536)
➌
Since the incident of Ifk occurred on the return from the Expedition of Banu Mustaliq,
therefore, at the end, the hadith of Ifk is mentioned, the details of which are as follows.

Hadith Commentary:
From this hadith, it is understood that if one has control over one's mount, then in any case, one should dismount and perform the obligatory prayer (fard salah) on the ground itself.
(And Allah knows best what is correct)

Hadith Commentary:
(1)
It is obligatory to face the qiblah in order to perform the obligatory prayer (salah). There is consensus (ijma‘) of the scholars of the ummah on this matter. This is the reason that performing the obligatory prayer on a mount (means of transport) is not valid; however, if someone is excused (ma‘dhur), then he is permitted. Nevertheless, in the prayer of fear (salat al-khawf), facing the qiblah is not required. In such emergency situations, the obligatory prayer can be performed facing whichever direction one is able. (Fath al-Bari: 2/742)

(2)
When performing voluntary (nafl) prayers on a mount, at the beginning, the mount should be turned towards the qiblah, then, whichever direction it turns afterwards, one may continue the prayer. As narrated from Anas radi Allahu anhu, when the Messenger of Allah sallallahu alayhi wa sallam intended to perform voluntary prayers during travel, he would turn his camel towards the qiblah, then, whichever direction it turned, he would remain engaged in his prayer. (Sunan Abi Dawud, Salat al-Safar, Hadith: 1225)

1⎋:
It should be clear that this permissibility is only for Sunnah and Nafl (supererogatory) prayers, not for obligatory (Fard) prayers.