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