When the people of Yemen came to the Messenger of Allah ﷺ, they asked him to send with them a man to teach them, so he sent Abu Ubayda with them and said, "He is the trustworthy one of this nation."
حدثنا يزيد بن هارون أخبرنا حماد بن سلمة عن ثابت البناني
أن أهل اليمن لما قدموا على رسول الله ﷺ سألوه أن يبعث معهم رجلا يعلمهم فبعث معهم أبا عبيدة وقال هو أمين هذه الأمة
Its isnad is sahih. The hadith with similar wording was narrated by Bukhari 5/32 in the Book of Virtues, chapter on the virtues of Abu Ubayda, and Muslim 4/1881 no. 2419 in the Book of the Virtues of the Companions, and Tirmidhi 5/167 no. 3796 similar to Bukhari's version, and he said, hasan sahih, and Ibn Majah in the Introduction 1/48 no. 135, similarly.