Bukhari

Hadith Commentary:
On the occasion of this battle, the Muslims neither had sufficient rations nor military equipment, and it was also a time of severe cold.
Within Madinah itself, the Jews were lying in ambush.
The disbelievers of Arabia had come together as a united front in great numbers, but on this occasion, the defense was carried out from within the city, and the city was secured by digging a trench.
Thus, by the grace of Allah, the disbelievers were not successful in their evil intentions and returned defeated, and their wicked ambitions for the future were also thwarted.
In this battle, Hudhayfah (radi Allahu anhu) went as a spy to gather intelligence about the disbelievers.
He came back and informed that the wind had overturned all the tents of the disbelievers and had even toppled their cooking pots, and that they had all fled.

Hadith Commentary:
1.
In this verse, the attack of the allied armies of the disbelievers is described: the disbelievers of Ghatafan, who were to the east of Madinah, attacked the Muslims from the upper side, and from the lower side, to the west, the disbelievers of Quraysh attacked—that is, the allied disbelievers had surrounded the Muslims.
In such circumstances, the Messenger of Allah (sallallahu alayhi wa sallam) went out with three thousand soldiers to confront them and positioned their backs towards the mountain of Sala‘ so that no attacker could come from behind.
He had a trench dug between himself and the disbelievers, and placed the women and children in a safe place on the hills. The siege of Madinah lasted for about twenty-five days, until Allah, the Exalted, sent a cold wind, causing the allied armies of the disbelievers to scatter and flee.

2.
The beginning of this battle was such that after the Battle of Uhud, the Battle of Banu Nadir took place, as a result of which the Jews were expelled from Madinah and they took refuge in Khaybar.
From among these exiled Jews, a delegation of twenty individuals came to the Quraysh of Makkah and encouraged them to launch a collective and decisive blow against the Muslims.
The disbelievers of Makkah agreed to this proposal of the Jewish delegation.
After this, the delegation went to Ghatafan.
Since this tribe was already an ally of the Jews, they immediately agreed as well.
Thereafter, this delegation went to other tribes hostile to the Muslims, until all the elements opposed to Islam were incited to wage war against the Muslims. Thus, in Dhu al-Qa‘dah, 5 AH, from the southern side, under the leadership of Abu Sufyan, the disbelievers of Quraysh, along with their allied tribes residing in Kinana and Tihamah, set out towards Madinah with an army of four thousand men.
At the place of Marr al-Zahran, the sub-tribes of Banu Sulaym also joined Abu Sufyan’s army.
From the eastern side, the Ghatafani tribes of Fazarah, Harrah, and Ashja‘ also joined this army.
In this way, by the time they reached Madinah, the number of this army had reached ten thousand, while the total population of Madinah was less than ten thousand.
Among them, only three thousand were fighting men, and even among these three thousand were included the hypocrites. If the Muslims had not dug the trench and defended themselves in time, this large army would have been sufficient to annihilate the Muslims in a single attack. It was in such circumstances that the aforementioned verse was revealed.
And Allah knows best.