It was narrated from Hudhaifah that:
The Messenger of Allah said to the people of Najran: "I will send you a trustworthy man with you, who is indeed trustworthy." The people craned their necks to see, and he sent Abu 'Ubaidah bin Jarrah. (ES)
English reference (ES): Vol. 1, Book 1, Hadith 135 (ES)
Arabic reference (ES): Book 1, Hadith 140 (ES)