Abdullah bin Masud reported,

Aqib and Sayyid, the two leaders of Najran, came intending to engage in mutual imprecation with the Messenger of Allah ﷺ. One of them said to his companion, "Do not engage in mutual imprecation with him. By Allah, if he is truly a prophet and we curse one another," (Khalaf said in his version, "and we engage in mutual imprecation,") "neither we nor our descendants will ever prosper."So they came to him and said, "We will not engage in mutual imprecation with you. Instead, we will give you what you have asked for. Send with us a trustworthy man."The Prophet ﷺ said, "I shall send with you a man who is truly trustworthy, truly trustworthy."The companions of Muhammad eagerly hoped to be chosen for this task. Then he said, "Stand up, Abu Ubayda bin al-Jarrah."When Abu Ubayda turned to leave, the Prophet ﷺ said, "This is the trustworthy one of this nation."

Azami 9976

Sahih

عن عبد الله بن مسعود قال

جاء العاقب والسيد صاحبا نجران، قال: وأرادا أن يلاعنا رسول الله ﷺ، قال: فقال أحدهما لصاحبه: لا تلاعنه، فوالله لئن كان نبيا، فلعنا- قال خلف: فلاعنا- لا نفلح نحن ولا عقبنا أبدا، قال: فأتياه، فقالا: لا نلاعنك، ولكنا نعطيك ما سألت فابعث معنا رجلا أمينا، فقال النبي ﷺ: لأبعثن رجلا أمينا حق أمين، حق أمين قال: فاستشرف لها أصحاب محمد، قال: فقال: قم يا أبا عبيدة بن الجراح قال: فلما قفى، قال: هذا أمين هذه الأمة.

الأعظمي 9976صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Virtues of the Companions and reports about them
Chapter
Virtues of Abu Ubayda bin Jarra and his reports
Section
Abu Ubayda being the trustworthy one of this ummah
Numbering
Jami al-Kamil 9976 (2nd edition)
Azami 9976