Musnad Ahmad 1007:2

Hushaym narrated to us, Yahya ibn Sa'id narrated to us, from 'Umar ibn Kathir ibn Aflah, from Abu Muhammad, a companion who used to sit with Abu Qatadah, he said: Abu Qatadah narrated to us that the Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever establishes clear evidence regarding a slain person, then for him is his spoils."