Musannaf Ibn Abi Shayba 36:102

Abdullah ibn Idris narrated to us, from Ibn Ishaq, from Muhammad ibn Ja'far ibn al-Zubayr, that the Messenger of Allah (may Allah bless him and grant him peace) sent Abdullah ibn Unays to Khalid ibn Sufyan. He said: "When I drew near to him—and that was at the time of Asr—I feared that there might be some intervention or struggle between us, so I prayed while I was walking."