Narrated Hudhaifah bin Al-Yaman:
that Al-'Aqib and As-Sayyid (two of the leaders of the Christians of Najran) came to the Prophet (ﷺ) and said: "Send us your trustworthy one." He said: "I shall send with you a trustworthy one who is truly a trustworthy one." So the people desired that, and he sent Abu 'Ubaidah, may Allah be pleased with him. (JA)
English reference (JA): Vol. 1, Book 46, Hadith 3796 (JA)
Arabic reference (JA): Book 49, Hadith 4165 (JA)