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