For every Umma there is a man of trust and the man of trust of this Umma is Abu 'Ubaida b. Jarrah.  

قَالَ رَسُولُ اللَّهِ ﷺ إِنَّ لِكُلِّ أُمَّةٍ أَمِينًا وَإِنَّ أَمِينَنَا أَيَّتُهَا الأُمَّةُ أَبُو عُبَيْدَةَ بْنُ الْجَرَّاحِ  

Send with us a person who should teach us Sunnah and al-Islam, whereupon he (the Holy Prophet) caught hold of the hand of Ubaida and said: He is a man of trust of this Umma.  

أَنَّ أَهْلَ الْيَمَنِ قَدِمُوا عَلَى رَسُولِ اللَّهِ ﷺ فَقَالُوا ابْعَثْ مَعَنَا رَجُلاً يُعَلِّمْنَا السُّنَّةَ وَالإِسْلاَمَ قَالَ فَأَخَذَ بِيَدِ أَبِي عُبَيْدَةَ فَقَالَ هَذَا أَمِينُ هَذِهِ الأُمَّةِ  

Messenger of Allah, send along with us a man of trust; whereupon he said: I would definitely send to you a man of trust, a man of trust in the true sense of the term. Thereupon his Companions looked up eagerly and he sent Abu Ubaida b. Jarrah.  

جَاءَ أَهْلُ نَجْرَانَ إِلَى رَسُولِ اللَّهِ ﷺ فَقَالُوا يَا رَسُولَ اللَّهِ ابْعَثْ إِلَيْنَا رَجُلاً أَمِينًا فَقَالَ لأَبْعَثَنَّ إِلَيْكُمْ رَجُلاً أَمِينًا حَقَّ أَمِينٍ حَقَّ أَمِينٍ قَالَ فَاسْتَشْرَفَ لَهَا النَّاسُ قَالَ فَبَعَثَ أَبَا عُبَيْدَةَ بْنَ الْجَرَّاحِ  

This hadith has been reported on the authority of Abu Ishaq with the same chain of transmitters.  

عَنْ أَبِي إِسْحَاقَ بِهَذَا الإِسْنَادِ نَحْوَهُ