From Sahih Bukhari (Hadith 3290):
Narrated `Aisha:On the day (of the battle) of Uhud when the pagans were defeated, Satan shouted, "O slaves of Allah! Beware of the forces at your back," and on that the Muslims of the front files fought with the Muslims of the back files (thinking they were pagans). Hudhaifa looked back to see his father "Al-Yaman," (being attacked by the Muslims). He shouted, "O Allah's Slaves! My father! My father!" By Allah, they did not stop till they killed him. Hudhaifa said, "May Allah forgive you." `Urwa said that Hudhaifa continued to do good (invoking Allah to forgive the killer of his father till he met Allah (i.e. died)
Reference: Bukhari 3290