Bukhari

Hadith Commentary:
This is evidence of the exceptional bravery, courage, and boldness of Khalid (radi Allahu anhu).

Hadith Commentary:
➊
The Battle of Mu'tah greatly increased the Muslims’ prestige and reputation, because their opponents, the Romans, were at that time the most powerful people on the face of the earth.
The Arabs considered confronting them tantamount to suicide; therefore, for a mere three thousand men to face an enormous army of two hundred thousand was nothing short of a marvel.
In this battle, only twelve Muslims were martyred, and the number of Romans killed is not known; however, from the aforementioned narration it is understood that a large number of them were consigned to Hell.
One can estimate, when alone in the hand of Khalid ibn al-Walid (radi Allahu anhu) nine swords broke, how many must have been killed and wounded.

➋
Hafiz Ibn Hajar (rahimahullah) has written that in this battle, the Muslims inflicted heavy losses on the Romans and killed many polytheists, and Khalid ibn al-Walid (radi Allahu anhu) not only protected the Muslims from harm but also personally participated in the battle, killing many polytheists and inflicting great losses upon them.
(Fath al-Bari: 7/646.)