Bukhari

Hadith Commentary:
Although angels descended in other battles as well, in Badr the angels actually fought.
Al-Bayhaqi has narrated that the blows of the angels could be recognized:
A strike on the neck and a mark on the fingertips resembling a burn from fire.
In the chain of narration of Ishaq, it is reported from Jubayr ibn Mut'im (radi Allahu anhu) that on the day of Badr, before the defeat of the disbelievers, I saw black ants descending from the sky.
These were angels, and immediately after their descent, the disbelievers were defeated.
In another narration, it is mentioned that a Muslim was going to strike a disbeliever on the day of Badr, when suddenly he heard the sound of a whip from the sky.
Someone was saying, "O Hayzum! Go forward," and then that disbeliever fell dead.

Hadith Commentary:
➊
This hadith shows that the attainment of virtue is due to participation in the Battle of Badr.

➋
Imam Bukhari rahimahullah has proven from this hadith that although angels participated in other battles as well, in the Battle of Badr they fought in an organized manner and were declared superior to other angels.

➌
First, Allah Ta’ala gave the glad tidings of the inclusion of one thousand angels, then of three thousand; when anxiety increased, He gave the good news of five thousand angels joining, whereas even a single angel would have been sufficient to finish their task. However, Allah Ta’ala comforted the Muslims and sent angels in human form to assist them.

➍
Hafiz Ibn Hajar rahimahullah states:
The disbelievers who were killed at the hands of the angels were different from other slain; there were marks on their necks and joints.
(Fath al-Bari: 7/388)
In a narration of Sahih Muslim, it is mentioned that a Muslim was running to kill a disbeliever when suddenly the sound of a whip striking was heard, and the disbeliever fell and died instantly.
The Messenger of Allah sallallahu alayhi wa sallam said:
“This was Allah’s help that came from the third heaven.”
(Sahih Muslim, al-Jihad, Hadith: 4588 (1763))