Allah says:

إِذْ تَسْتَغِيثُونَ رَبَّكُمْ فَاسْتَجَابَ لَكُمْ أَنِّي مُمِدُّكُم بِأَلْفٍ مِّنَ الْمَلَائِكَةِ مُرْدِفِينَ ﴿٩﴾ وَمَا جَعَلَهُ اللَّـهُ إِلَّا بُشْرَىٰ وَلِتَطْمَئِنَّ بِهِ قُلُوبُكُمْ ۚ وَمَا النَّصْرُ إِلَّا مِنْ عِندِ اللَّـهِ ۚ إِنَّ اللَّـهَ عَزِيزٌ حَكِيمٌ ﴿١٠﴾

Iz tastagheethoona Rabbakum fastajaaba lakum annee mumiddukum bi-alfim-minal-malaaa'ikati murdifeen. Wa maa ja'alahullaahu illaa bushraa wa litatmainna bihee quloobukum; wa man-nasru illaa min 'indillaah; innallaaha 'Azeezun Hakeem.

(9) [Remember] when you asked help of your Lord, and He answered you, "Indeed, I will reinforce you with a thousand from the angels, following one another." (10) And Allah made it not but good tidings and so that your hearts would be assured thereby. And victory is not but from Allah. Indeed, Allah is Exalted in Might and Wise.

Reference: Surah Al-Anfal 8: 9-10