Musnad Ahmad 1034:33

Waki' narrated to us, from Sufyan, from Abu Ishaq, from Silah ibn Zufar, from Hudhayfah, who said: The Sayyid and the 'Aqib came to the Prophet, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, send with us your trustworthy one." Waki' said once: "a trustworthy one." He said: "I will send with you a trustworthy one, truly a trustworthy one." He said: So the people aspired to it, but he sent Abu Ubaydah ibn al-Jarrah.