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