وَإِذْ غَدَوْتَ مِنْ أَهْلِكَ تُبَوِّئُ الْمُؤْمِنِينَ مَقَاعِدَ لِلْقِتَالِ وَاللَّهُ سَمِيعٌ عَلِيمٌ ﴿۱۲۱﴾ إِذْ هَمَّتْ طَائِفَتَانِ مِنْكُمْ أَنْ تَفْشَلَا وَاللَّهُ وَلِيُّهُمَا وَعَلَى اللَّهِ فَلْيَتَوَكَّلِ الْمُؤْمِنُونَ ﴿۱۲۲﴾ وَلَقَدْ نَصَرَكُمُ اللَّهُ بِبَدْرٍ وَأَنْتُمْ أَذِلَّةٌ فَاتَّقُوا اللَّهَ لَعَلَّكُمْ تَشْكُرُونَ ﴿۱۲۳﴾ إِذْ تَقُولُ لِلْمُؤْمِنِينَ أَلَنْ يَكْفِيَكُمْ أَنْ يُمِدَّكُمْ رَبُّكُمْ بِثَلَاثَةِ آلَافٍ مِنَ الْمَلَائِكَةِ مُنْزَلِينَ ﴿۱۲۴﴾

﴾121﴿ Wa iz ghadawta min ahlika tubawwi'ul mu'mineena maqaa'ida lilqitaal; wallaahu samee'un 'aleem
﴾122﴿ Iz hammat taaa'ifataani minkum an tafshalaa wallaahu waliyyuhumaa; wa 'alal laahi falyatawakkalil mu'minoon
﴾123﴿ Wa laqad nasarakumul laahu bi-Badrinw wa antum azillatun fattaqul laaha la'allakum tashkuroon
﴾124﴿ Iz taqoolu lilmu'mineena alai yakfiyakum ai-yumiddakum Rabbukum bisalaasati aalaafim minal malaaa'ikati munzaleen

﴾121﴿ And when you went forth early in the morning from your home, assigning to the believers their positions for battle, and Allah the Exalted is All-Hearing, All-Knowing of everything.
﴾122﴿ When two groups among you were about to lose heart, but Allah the Exalted gave them courage and support — and upon Allah alone should the believers place their trust.
﴾123﴿ Indeed, Allah helped you at Badr when you were few in number. So fear Allah, so that you may be grateful
﴾124﴿ When you said to the believers, “Does it not suffice you that your Lord should help you with three thousand angels sent down?”

[121] In this verse, there is a reference to the Battle of Uhud. The connection with the previous discussion is that, during this incident, your patience faltered when hardship befell you, and some of the previously mentioned principles were neglected, which resulted in defeat.
(مِنْ أَهْلِكَ): In some narrations, it is mentioned that the Prophet (May Allah bless him and give him peace) set out for Uhud after the Zuhr (midday) prayer, so the reconciliation is that he left the house of ʿĀ’ishah (may Allah be pleased with her) before Zuhr, and after the prayer, he set out for Uhud, leading the army to battle. [122] Banū Ḥāritha and Banū Salamah (from among the Anṣār) were the two groups who intended to turn back on the way to Uhud, but then, through Allah’s inner help, they stood firm. This indicates that the Prophet (May Allah bless him and give him peace) fulfilled his duty completely; rather, the shortcoming was from his companions.
Himmah (resolve) refers only to intention that does not reach the level of firm decision, and this is not considered a sin.
(وَلِيُّهُمَا): A companion from these tribes said, “We are not saddened by the revelation of this verse, because this phrase waliyuhumā (their Protector) is such a mighty and noble statement.”
[123] The connection is that this is a response to the misconception that Allah did not grant victory to the believers at Uhud because their religion was not pleasing to Allah. The answer is that Allah had granted them victory at Badr because of their adherence to the faith. In this verse, the second event mentioned is the Battle of Badr, where the companions (may Allah be pleased with them) stood firm on previous principles and were mature in patience and piety, so with Allah's help they succeeded. The Battle of Badr took place one year before Uhud, in the month of Ramadan, while Uhud was in Shawwal. The detailed account of the Battle of Badr is in Surah al-Anfal. "And you were few and humble" means you were small in number, about three hundred and thirteen, and likewise you had few horses and little weaponry. "So fear Allah, so that you may be grateful"—meaning, the habit of gratitude is achieved through piety.
[124] For help, one thousand angels had been sent down, as mentioned in verse (9) of Surah Al-Anfal.
Then, when the disbelievers began to boast and threaten that another army was coming for them, Allah comforted the believers with another promise of help.
First, He promised three thousand angels.