The Repentance - 9:40
"If you do not help him, Allah has helped him. (For example) the disbelievers drove him out as the second of the two. And when the two of them were in the cave, he used to say to his companion, "Do not grieve, Allah is with us"... Allah sent down on him peace and security and humbled the word of the disbelievers by supporting them with armies you did not see. Exalted is the word of Allah alone. Allah is the Exalted, the Wise."
Peace and comfort descending upon the believers in battle:
The Family Of Imran/3:153
You were climbing the hill without looking back at anyone, although the Messenger called you from behind. He gave you sorrow upon sorrow so that you might not grieve for what you had lost and what had happened to you. Allah is All-Knowing of what you do.
The Family Of Imran/3:154
"Then after that sorrow, He sent down upon you a safe sleep which calmed a group of you. Some of you were self-absorbed and self-centered, forming false ideas about Allah, as in the days of ignorance, and saying, "Do we have any authority in this matter?"Say, "All authority belongs to Allah."They were hiding in their hearts what they did not reveal to you. They say, "If we had any authority, we would not have been killed here."Say, "Even if you had been in your homes, those among you who were appointed to die would have crawled to the place where they would have fallen."Allah thus tries what is in your breasts and purifies what is in your hearts. Allah knows the most secret thoughts."
The Spoils of War/8:9
"You were pleading with your Lord to save you, and He answered you, "I will support you with a thousand angels, one after the other"."
The Spoils of War/8:11
He was lulling you to sleep as a security from Himself, and He was sending down upon you water from the sky to cleanse you (from the depression of thirst), to drive away from you the filth of Satan (despair), to convince your hearts and to strengthen your feet.
The Spoils of War/8:12
"Your Lord revealed to the angels (and therefore to the believers): "I am with you, support those who believe. I will strike fear into the hearts of the disbelievers, strike their necks, strike every finger of their hands."
The Spoils of War/8:13
Because they actively fought against Allah and His messenger. Whoever fights against Allah and His messenger, surely the punishment of Allah is severe.
The Repentance/9:25
Allah helped you on many occasions. On the day of Hunayn you were proud of your numbers. But your numbers did you no good. Indeed, the earth became narrow for you despite its vastness and you turned and fled.
The Repentance/9:26
Then Allah sent down on His Apostle and the believers security and comfort from Himself, and He sent down armies that you did not see, and so He punished the disbelievers. This is the punishment of the disbelievers.
The Repentance/9:40
"If you do not help him, Allah has helped him. (For example) the disbelievers drove him out as the second of the two. And when the two of them were in the cave, he used to say to his companion, "Do not grieve, Allah is with us"... Allah sent down on him peace and security and humbled the word of the disbelievers by supporting them with armies you did not see. Exalted is the word of Allah alone. Allah is the Exalted, the Wise."
The Coalition/33:9
O you who believe, when armies attack you, remember the favor of Allah, Who sends upon you a wind and armies that you do not see. Allah is All-Seeing of all that you do.