Narrated Anas bin Malik:
"My paternal uncle was absent from the fighting of Badr, so he said: 'I was absent from the first fight the Messenger of Allah (ﷺ) fought with idolaters, so if Allah grants me to participate in a fight with the idolaters, then Allah will see what I will do!' So on the Day of Uhud, when the Muslims were driven back he said: 'O Allah! Indeed I am innocent before you of what these people - meaning the idolaters - have done, and I beg of You to excuse these people for what they have done - meaning the Companions. Then he went forward and met up with Sa'd. He said: 'O my brother! Whatever you do, I am with you!' But he was not able to do the same as him. He was found with more than eighty wounds, between blows with the sword, thrusts of a spear, or arrow wounds. We would say: 'It was about him and his companions that (the following) was revealed: 'Of them some have fulfilled their vow, and some of them are still waiting, but they have never changed in the least (33:23). (One of the narrators) Yazid said: "Meaning this Ayah."
English reference: Vol. 5, Book 44, Hadith 3201
Arabic reference: Book 47, Hadith 3506