Abd al-Rahman bin Abdullah bin Mas'ud narrates from his father, Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him), that he said: On the day of Badr I was sent to Abu Jahl, who had been left sitting (wounded). I took his sword and struck his head with it, and he said: "Our little shepherd of Makkah?" Then I struck him with his own sword until he grew cold (died). Then I came to the Prophet (peace and blessings be upon him) and said: "O Messenger of Allah, I have killed Abu Jahl." At this Aqil, who was a captive with the Prophet (peace and blessings be upon him), said: "You lie; you did not kill him." I said: "Rather, you are the sinful liar, O enemy of Allah! By Allah, it was I who killed him." He said: "What is his mark?" I said: "On his thigh there is a mark like the mark on a camel's knee." He said: "You have spoken the truth."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8444