Uḥud

Quraysh came back with three thousand men to answer Badr. He ﷺ preferred to defend inside the city; the younger men who had missed Badr wanted to go out, and he went with the majority — and did not change his mind after putting on his armour, even when they regretted it. On the way ʿAbdullāh ibn Ubayy turned back with three hundred men.

He placed fifty archers on a hill with one instruction: do not leave, whatever happens, even if you see birds carrying us away. The Muslims broke the Makkan lines; the archers saw the enemy fleeing and came down for the spoils; Khālid ibn al-Walīd, still an opponent, took the cavalry round the exposed flank. Seventy Muslims were killed including Ḥamzah رضي الله عنه, whose body was mutilated; the Prophet ﷺ was wounded in the face and a tooth was broken, and word spread that he had been killed.

Sūrat Āl ʿImrān goes through the day step by step and tells them the loss came from themselves. Study this year whenever you want to know how Islam handles defeat: name the cause, refuse despair, and go out again the next morning to Ḥamrāʾ al-Asad.