Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: I reached Abu Jahl while he lay struck down. He had his helmet on and a fine sword with him, while I had a poor (worn-out) sword. I began striking his head with my sword, remembering how he used to strike my head in Makkah, until his hand grew weak and I took his sword. He raised his head and said: Against whom did the turn of fortune (defeat) fall, in our favour or against us? Were you not our little shepherd in Makkah? Then I killed him. Then I came to the Prophet (peace and blessings be upon him) and said: "I have killed Abu Jahl." He (peace and blessings be upon him) said: "By Allah, besides whom there is no god?" and he made me swear three times. Then he stood up and went with me to them, and supplicated against them.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8438