Musnad Abu Ya'la al-Mawsili 152:195

Muhammad ibn Abi Bakr narrated to us, 'Atham ibn 'Ali narrated to us, from al-A'mash, from Abu Ishaq, from Abu 'Ubaydah, from 'Abdullah, who said: I reached Abu Jahl while he was fallen, wearing a helmet. I had with me a worn-out sword, so I began to strike his head with my sword, recalling a striking he used to strike my head with in Makkah, until his hand weakened. I took his sword, and he raised his head and said: "Against whom was the victory? Against us or for us? Are you not the little shepherd of Makkah?" He said: So I killed him. Then I came to the Prophet, peace and blessings of Allah be upon him, and said: "I have killed Abu Jahl." He said: "By Allah, besides whom there is no god, have you killed him?" He asked me to swear three times. Then he stood up with me to them and invoked [curses] against them.