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. (AR)
English reference (AR): Vol. 1, Book 1, Hadith 135 (AR)
Arabic reference (AR): Book 1, Hadith 140 (AR)