The son of Sayyiduna Abdullah bin Unays (may Allah be pleased with him) narrates from his father that he said: The Messenger of Allah (peace and blessings be upon him) sent me to Khalid bin Sufyan, who was in the direction of Uranah and Arafat, and he (peace and blessings be upon him) said: "Go and kill him." He says: I saw him, and at that moment the time of the Asr prayer came. I thought: I fear that the matter between me and him will cause the prayer to be delayed. So I set off towards him praying as I walked, making gestures (for bowing and prostration). When I came near him, he said to me: Who are you? I said: An Arab; news has reached me that you are gathering an army against this man, so I too have come to you for that purpose. He said: I am doing exactly that. So I walked with him for a while, and when I got my chance against him, I attacked him with my sword until he died.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17884