Bukhari

Hadith Commentary:
What happened was that in the 8th year after Hijrah, the Prophet sallallahu alayhi wa sallam dispatched an army for the Battle of Mu'tah.
He appointed Zayd ibn Harithah radi Allahu anhu as its commander and said: If he is martyred, then make Ja'far radi Allahu anhu the commander; if he too is martyred, then Abdullah ibn Rawahah radi Allahu anhu should be made the commander.
Coincidentally, these three commanders were martyred one after the other, and Khalid ibn al-Walid radi Allahu anhu finally took up the standard of leadership so that the Muslims would not lose heart, as the battle had become very intense.
Although the Prophet sallallahu alayhi wa sallam had not said anything regarding him (Khalid).
He (Khalid) fought the disbelievers to such an extent that Allah granted victory to the army of Islam through him.
In another narration, it is mentioned that the Prophet sallallahu alayhi wa sallam, pleased with Khalid, said regarding him that he is one of the swords of Allah.
Further details will come under the mention of the Battle of Mu'tah.

Hadith Commentary:
➊
When the martyrs witnessed the honor and greatness bestowed upon them by Allah due to their martyrdom, they no longer wished to return to the world. In this hadith, there is evidence of prophethood, as the Messenger of Allah (sallallahu alayhi wa sallam) informed about the martyrdom of these individuals while he was present in Madinah Tayyibah at that time.

➋
When Khalid ibn al-Walid (radi Allahu anhu) saw that these individuals had been martyred, he thought that if the Muslims remained in this state, they would be destroyed and the strength of Islam would suffer a severe blow. Therefore, he took the commander's flag into his own hands on his own initiative so that the Muslims would not lose courage. Then he launched a fierce attack until Allah, the Exalted, granted him victory. The Messenger of Allah (sallallahu alayhi wa sallam) was also pleased with this action, even though he had not appointed him as commander, nor had anyone in the army pledged allegiance to him.

➌
From this, it is understood that in times of necessity, the conditions of the Shari'ah rulings can be relaxed.

And Allah knows best.

Hadith Commentary:
➊
This incident pertains to the Battle of Mu'tah, which took place in Jumada al-Ula, 8 AH.
If such a critical time befalls Islam that the battlefield is slipping from the hands of the Muslims and the Muslim leadership is also coming to an end, then it is permissible for any person of insight and one acquainted with the secrets and strategies of war to immediately take command. This is as, in the Battle of Mu'tah, after the martyrdom of all three commanders, Khalid ibn al-Walid (radi Allahu anhu) took the banner into his own hands on his own initiative, while the fierce battle was ongoing and the Muslims were fiercely confronting the enemy. If, in such circumstances, no one had picked up the banner, the enemy would have prevailed, and the Muslims would have suffered such an irreparable blow to their strength that it would not have been good in any way.

➋
Not only did the Messenger of Allah (sallallahu alayhi wa sallam) approve of this action, but he also declared Khalid ibn al-Walid (radi Allahu anhu) to be the Sword of Allah and gave the glad tidings of victory at his hands to the noble Companions (radi Allahu anhum).
This does not undermine the Islamic system of leadership (imarah); rather, it is evidence of its comprehensive and expansive nature, in that, in such grave and emergency situations, an excellent and acceptable solution has been indicated.
And Allah knows best.

Hadith Commentary:
➊
The Messenger of Allah (sallallahu alayhi wa sallam) declared Khalid ibn al-Walid (radi Allahu anhu) to be the Sword of Allah.
Indeed, he was truly the Sword of Allah; wherever he went, victory and triumph followed in his footsteps.
The Messenger of Allah (sallallahu alayhi wa sallam) supplicated for him in these words:
“O Allah! He is one of Your swords, so help him.”
(Musnad Ahmad: 8/1)

➋
The incident mentioned in the hadith pertains to the Battle of Mu’tah.
(Tabaqat Ibn Sa’d: 7/395)

Hadith Commentary:
This is the incident of the Battle of Mu'tah, which took place in 8 AH on the land of Balqan near the region of al-Sham (Greater Syria).
The Muslims numbered three thousand, while the disbelievers were countless. The Prophet (sallallahu alayhi wa sallam) appointed Zayd ibn Harithah as the commander of the army and stated that if Zayd were to be martyred, then Ja'far (radi Allahu anhu) should take command, and if he too were martyred, then Abdullah ibn Rawahah.
All three of these leaders were martyred.
Then Khalid ibn al-Walid (radi Allahu anhu) (on his own initiative) took up the command, and (by Allah’s will, through his hands) the disbelievers were decisively defeated. The Noble Prophet (sallallahu alayhi wa sallam) informed the people of all these events even before the army returned.
In this hadith, several miracles of the Prophet (sallallahu alayhi wa sallam) are also mentioned.

Hadith Commentary:
(1)
The hadith prohibits "na‘yi," by which is meant announcing or proclaiming death. Hudhayfah (radi Allahu anhu) narrated that the Messenger of Allah (sallallahu alayhi wa sallam) used to forbid announcing death. (Musnad Ahmad: 406/5) Hudhayfah (radi Allahu anhu) said that when he passed away, no one should be informed about him, because there was a fear of "na‘yi," which the Messenger of Allah (sallallahu alayhi wa sallam) had prohibited. (Jami‘ at-Tirmidhi, Al-Jana’iz, Hadith: 986) However, the "na‘yi" which the Shari‘ah has prohibited was the "na‘yi" of the people of Jahiliyyah, in which people would send announcers to inform others of the death, who would proclaim at the doors of houses and in the markets, including wailing and mention of the deceased’s praiseworthy deeds. The notification and similar acts whose permissibility Imam al-Bukhari (rahimahullah) is establishing have no connection with the "na‘yi" of Jahiliyyah.

(2)
From multiple ahadith, three situations regarding the announcement of death can be derived:
٭ Informing the household, companions, relatives, and righteous people is Sunnah.
٭ Informing a large group for the sake of pride, ostentation, or boasting is a disliked act.
٭ Any announcement that involves wailing or similar acts is prohibited (haram) and against the Shari‘ah.
By "wailing" (nawh), it is meant to enumerate the qualities and characteristics of the deceased loudly, to cry, beat oneself, and to scream and shout while recalling their great achievements.

(3)
From this hadith, Imam al-Bukhari (rahimahullah) has established that informing the relatives and close ones of the deceased about the death is not prohibited. The Messenger of Allah (sallallahu alayhi wa sallam) himself informed the families and religious associates of the martyrdom of Zayd, Ja‘far, and ‘Abdullah ibn Rawahah (radi Allahu anhum). (Fath al-Bari: 151/3)

(4)
The Messenger of Allah (sallallahu alayhi wa sallam) did not appoint Khalid ibn al-Walid (radi Allahu anhu) as the commander of the army, yet he assumed command and inflicted a crushing defeat upon the disbelievers. In grave circumstances, such action is permissible.