Sahih Muslim 1733 a
It has also been narrated by Sa'd b. Abu Burda through his father through his grandfather that the Prophet of Allah (ﷺ) sent him and Mu'adh (on a mission) to the Yemen, and said (by way of advising them):
Show leniency (to the people) ; don't be hard upon them; give them glad tidings (of Divine favours in this world and the Hereafter) ; and do not create aversion. Work in collaboration and don't be divided.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا وَكِيعٌ، عَنْ شُعْبَةَ، عَنْ سَعِيدِ بْنِ أَبِي بُرْدَةَ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، أَنَّ النَّبِيَّ صلى الله عليه وسلم بَعَثَهُ وَمُعَاذًا إِلَى الْيَمَنِ فَقَالَ ‏
"‏ يَسِّرَا وَلاَ تُعَسِّرَا وَبَشِّرَا وَلاَ تُنَفِّرَا وَتَطَاوَعَا وَلاَ تَخْتَلِفَا ‏"‏ ‏.‏