Then Allah sent down His tranquility upon His Messenger:

Meaning, His mercy, through which hearts become tranquil and attain absolute reassurance, which is followed by imminent victory. As for tranquility in the absolute sense, it had already been attained by him (may Allah exalt him and grant him peace).

And upon the believers:

This is a conjunction linked to "His Messenger." The repetition of the preposition [‘ala – upon] is to signify the difference in degree [between the two]. Those intended here are the ones who had fled [in defeat]. This indicates that [numerical] majority does not negate faith. According to al-Hasan, they are those who remained steadfast with the Messenger of Allah (may Allah exalt him and grant him peace). It has also been said that the intended meaning encompasses both groups, which is not without merit; there is no harm in the original tranquility being realized in the steadfast ones beforehand.

Some interpreted tranquility as security. For him (may Allah exalt him and grant him peace), it was through witnessing the angels (peace be upon them); for those with him, through the manifestation of signs of that [divine support]; and for those who fled, by the removal of their anxiety and agitation through the realization that what Allah wills happens, and what He does not will does not happen, or similar reflections.

The apparent meaning is that "then" (thumma) is in its place to indicate a delay [in time] between the flight and the sending down of tranquility in this manner. It has also been said: if the believers intended are those who fled, then it is in its proper place; if the steadfast are intended, then the delay is in the reporting [of the events], or it pertains to the sum of this descent and what is conjoined to it. Considering it a delay of rank is far-fetched.

And He sent down soldiers you did not see:

With your eyesight, the way you see one another. They are the angels (peace be upon them) riding piebald horses, wearing white. That the intended meaning is "you did not see their like before that" is contrary to the apparent sense, and we have not seen any reports that support it.

There is a difference of opinion regarding their number. It is said: eight thousand, based on His saying: "Will it not suffice you that your Lord should reinforce you with three thousand..." along with His saying afterward: "Your Lord will reinforce you with five thousand." It is also said: five thousand, as per the second verse, with the initial three thousand being included in these five. It is also said: sixteen thousand, equaling the number of both armies—twelve thousand from the Muslim army and four thousand from the polytheists' army.

Likewise, they differed on whether they fought in this battle or not. The majority hold that the angels did not fight except on the day of Badr, and that they only descended to strengthen the hearts of the believers by instilling good thoughts and supporting them through that, and by casting terror into the hearts of the polytheists.

It is narrated from Sa’id ibn al-Musayyib who said: A man who was among the polytheists on the day of Hunayn told me: "When we exposed [the weakness of] the Muslims, we began to drive them back. When we reached the man on the grey mule, we were met by men with white faces who said: 'May the faces be disfigured! Go back!' So we turned back, and they [the Muslims] rode upon our backs."

Those who argued that they did fight cited the report that a man from among the polytheists said to one of the believers after the fighting: "Where were the piebald horses and the men wearing white clothes? We did not see them among you except like a mole [on a face], and our killing was only at their hands." The Messenger of Allah (may Allah exalt him and grant him peace) was informed of this, and he (upon him be peace and prayer) said: "Those were the angels." However, this has no chain of transmission to rely upon.

And He punished those who disbelieved:

Through killing, capture, and taking them as slaves.

And that:

Meaning, what was done to them from what has been mentioned.

Is the recompense of the disbelievers:

For their disbelief in the worldly life.