Sahih Bukhari Volume 008, Book 078, Hadith Number 661.

Narated By 'Aisha : When the pagans were defeated during the (first stage) of the battle of Uhud, Satan shouted, "O Allah's slaves! Beware of what is behind you!" So the front files of the Muslims attacked their own back files. Hudhaifa bin Al-Yaman looked and on seeing his father he shouted: "My father! My father!" By Allah! The people did not stop till they killed his father. Hudhaifa then said, "May Allah forgive you." 'Urwa (the sub-narrator) added, "Hudhaifa continued asking Allah forgiveness for the killers of his father till he met Allah (till he died)."