Al-Ahzaab 33:9

O you who believe, remember Allah’s favor upon you when [enemy] forces came against you[7], but We sent against them a violent wind and forces that you could not see[8]. And Allah is All-Seeing of what you do.

[7] This is referring to what is known as the Battle of the Trench or the Confederates which occurred in 5 A.H./627 C.E., where the pagans of Makkah along with some Arab and Jewish tribes (totaling around 10,000 soldiers) besieged Madinah, and the Prophet (ﷺ) positioned around 3000 soldiers to defend Madinah. The Prophet (ﷺ) had anticipated the offense and, upon advice from one of his companions, Salmān from Persia, dug a trench around the city to protect it from the invaders. After several attempts to cross the trench, the Allied forces lost morale and were forced to end the siege due to severe weather conditions. By this Allah saved Muslims from the machination of the non-Muslim allied forces to destroy the newly-born Islamic community in Madinah.
[8] i.e., the angles.

O you who have believed, remember the favor of Allāh upon you when armies came to [attack] you and We sent upon them a wind and armies [of angels] you did not see. And ever is Allāh, of what you do, Seeing.

9. O you who believe! Remember Allâh’s Favour to you, when there came against you hosts, and We sent against them a wind and forces that you saw not [i.e. troops of angels during the battle of Al-Ahzâb (the Confederates)]. And Allâh is Ever All-Seer of what you do.

O ye who believe! Remember Allah's favour unto you when there came against you hosts, and We sent against them a great wind and hosts ye could not see. And Allah is ever Seer of what ye do.