Musnad Ahmad 265:7

Yahya ibn Adam narrated to us, he said: Ibn Idris narrated to us, from Muhammad ibn Ishaq, from Muhammad ibn Ja’far ibn al-Zubayr, from some of the children of Abdullah ibn Unays, from the family of Abdullah ibn Unays, that the Messenger of Allah (peace and blessings of Allah be upon him) sent him to Khalid ibn Sufyan ibn Nubayh al-Hudhali to kill him, for he was gathering [forces] to fight the Messenger of Allah (peace and blessings of Allah be upon him). He said: So I came to him at ‘Arana while he was with some of his livestock, and the time for Asr had entered. I feared that there would be a struggle between me and him that would distract me from the prayer. He said: So I prayed while I was walking, gesturing with a gesture. When I reached him, I said such and such—until he mentioned the rest of the hadith. Then he came to the Prophet (peace and blessings of Allah be upon him) and informed him of his killing of him, and he mentioned the hadith.