The verses below speak of a historical incident at Prophet Muhammed’s (p) life-time. These verses allude to an incident just after the Battle of Uhud. Some scholars say the verse refers to Hamra al-Asad, others say these verse allude an incident a year after the battle of Uhud, called the ‘lesser Badr‘.
3:172 Those [believers] who responded to Allah and the Messenger after injury had struck them. For those who did good among them and feared Allah is a great reward –
3:173 Those to whom hypocrites said, “Indeed, the people have gathered against you, so fear them.” But it [merely] increased them in faith, and they said, “Sufficient for us is Allah, and [He is] the best Disposer of affairs.”
In Quran 3:172 it mentions the latter part battle of Uhud, when the Quraysh won the battle and went back towards Makkah. There was a debate among the Quraysh to go back and slaughter more Muslims. At the same time, some of the Muslims who were still alive – didn’t get killed, were in pursuit of those criminals who had slaughtered Muslims in the battle, 1400 years ago. At the end of the verse, God says, that he will reward them for their works.
Tafhim al-Qur’an – Sayyid Abul Ala Maududi:
“122 This verse alludes to those devoted servants of Islam who willingly accompanied the Holy Prophet in his pursuit of the Quraish at that critical juncture. After the Battle of Uhud, the Quraish marched back towards Makkah. When they had covered a good deal of distance from Al-Madinah, they realized that they had not utilised the golden opportunity of crushing the power of Muhammad (Allah’s peace be upon him) and they began to regret: what a folly have we committed by losing that excellent chance! Accordingly, they halted and held a council of war. Though they were in favour of returning to Al-Madinah and making a sudden attack, yet they could not muster up courage and continued their march towards Makkah. At the same time, the Holy Prophet surmised an attack from the enemy; so he assembled the Muslims on the next day after the battle of Uhud and said, “Let us go in pursuit of the Quraish.” Although that was a very critical situation, yet the believers and the devoted servants of Allah responded to the call and willingly marched with the Holy Prophet to Hamra-ul-Asad, a place at a distance of 8 miles from Al-Madinah.” 
Maulana Muhammad Ali:
“172a. The Makkan army was pursued the next day to a place known as Hamra’ al-Asad, under which name the expedition is known. Such was the spirit of invincibility of the Muslim army even after the loss suffered at Uhud.” 
“130 Lit., “after injury had afflicted them”. Most of the commentators assume that this is an allusion to the losses sustained by the Muslims at the battle of Uhud. It is, however, probable that the implication is much wider, the more so since this passage connects directly with the preceding verses which speak, in general terms, of the martyrs who die in God’s cause. There is a distinct tendency on the part of most of the classical commentators to read minute historical references into many Qur’anic passages which express ideas of a far wider import and apply to the human condition as such. Verses 172-175 are an instance of this. Some commentators are of the opinion that they refer to the fruitless expedition to Hamra’ al-Asad on the day following the battle of Uhud, while others see in it an allusion to the Prophet’s expedition, in the following year, known to history as the “Little Badr” (Badr as-Sughra); others, again, think that verse 172 refers to the former and verses 173-174 to the latter. In view of this obvious lack of unanimity – due to the absence of a really authoritative support, either in the Qur’an itself or in authentic Traditions, for any of these speculative assumptions – there is every reason for concluding that the whole passage under consideration expresses a general moral, rounding off, as it were, the historical references to the battle of Uhud and the lessons to be drawn therefrom.” 
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 Sayyid Abul Ala Maududi – Tafhim al-Qur’an – The Meaning of the Qur’an
 The Holy Quran Arabic Text with English Translation, Commentary and comprehensive Introduction [Year 2002 Edition] by Maulana Muhammad Ali, page 183
 The Message of The Quran translated and explained by Muhammad Asad, page 148