Umar ibn al-Khattab reported: On the day of Badr, the Messenger of Allah, peace and blessings be upon him, looked upon the idolaters and they were a thousand in number, while his companions were only three hundred and nineteen men. The Prophet faced the direction of prayer, then he raised his hands and supplicated aloud to his Lord, “O Allah, accomplish what You have promised me! O Allah, bring about what You have promised me! O Allah, if this band among the people of Islam is destroyed, You will not be worshipped on the earth!” The Prophet continued to call out to his Lord with his hands raised and facing the direction of prayer until his cloak fell from his shoulders. Abu Bakr came, picked up his cloak, and placed it on his shoulders, then he embraced him from behind, saying, “O Prophet of Allah, your supplication to your Lord will suffice, for He will accomplish what He has promised you.” Allah Almighty revealed the verse, “When you sought deliverance from your Lord and He answered you: Verily, I will reinforce you with a thousand angels, rank after rank,” (8:9). Thus, Allah reinforced him with the angels.
Source: Ṣaḥīḥ Muslim 1763
Grade: Sahih (authentic) according to Muslim
عَنْ عُمَرُ بْنُ الْخَطَّابِ قَالَ لَمَّا كَانَ يَوْمُ بَدْرٍ نَظَرَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ إِلَى الْمُشْرِكِينَ وَهُمْ أَلْفٌ وَأَصْحَابُهُ ثَلَاثُ مِائَةٍ وَتِسْعَةَ عَشَرَ رَجُلًا فَاسْتَقْبَلَ نَبِيُّ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ الْقِبْلَةَ ثُمَّ مَدَّ يَدَيْهِ فَجَعَلَ يَهْتِفُ بِرَبِّهِ اللهُمَّ أَنْجِزْ لِي مَا وَعَدْتَنِي اللهُمَّ آتِ مَا وَعَدْتَنِي اللهُمَّ إِنْ تُهْلِكْ هَذِهِ الْعِصَابَةَ مِنْ أَهْلِ الْإِسْلَامِ لَا تُعْبَدْ فِي الْأَرْضِ فَمَا زَالَ يَهْتِفُ بِرَبِّهِ مَادًّا يَدَيْهِ مُسْتَقْبِلَ الْقِبْلَةِ حَتَّى سَقَطَ رِدَاؤُهُ عَنْ مَنْكِبَيْهِ فَأَتَاهُ أَبُو بَكْرٍ فَأَخَذَ رِدَاءَهُ فَأَلْقَاهُ عَلَى مَنْكِبَيْهِ ثُمَّ الْتَزَمَهُ مِنْ وَرَائِهِ وَقَالَ يَا نَبِيَّ اللهِ كَفَاكَ مُنَاشَدَتُكَ رَبَّكَ فَإِنَّهُ سَيُنْجِزُ لَكَ مَا وَعَدَكَ فَأَنْزَلَ اللهُ عَزَّ وَجَلَّ إِذْ تَسْتَغِيثُونَ رَبَّكُمْ فَاسْتَجَابَ لَكُمْ أَنِّي مُمِدُّكُمْ بِأَلْفٍ مِنَ الْمَلَائِكَةِ مُرْدِفِينَ فَأَمَدَّهُ اللهُ بِالْمَلَائِكَةِ
1763 صحيح مسلم كتاب الجهاد والسير باب الإمداد بالملائكة في غزوة بدر وإباحة الغنائم