Musannaf Ibn Abi Shayba 36:484

'Abd al-Rahim ibn Sulayman narrated to us, from Zakariyya, from Abu Ishaq, from Silah ibn Zufar, from Hudhayfah, who said: The two bishops of Najran, al-'Aqib and al-Sayyid, came to the Prophet, peace and blessings of Allah be upon him. They said, "Send with us a man who is trustworthy, truly trustworthy, truly trustworthy." He said, "I will surely send with you a man who is truly trustworthy." The companions of Muhammad craned their necks for it. He said, "Stand up, O Abu 'Ubaydah ibn al-Jarrah," and he sent him with them.