It is narrated from Hazrat Anas (may Allah be pleased with him) that when the people of Yemen came to the service of the Prophet (peace and blessings be upon him), they requested the Prophet (peace and blessings be upon him) to send a man with them who would teach them the religion. The Prophet (peace and blessings be upon him) said, "I will send with you the trustworthy one of this Ummah." Then the Prophet (peace and blessings be upon him) sent Hazrat Abu Ubaidah (may Allah be pleased with him) with them.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 12789
Hadith Gradingحکم دارالسلام:حديث صحيح، م: 2419، وهذا إسناد ضعيف لضعف مؤمل بن إسماعيل، وقد توبع