Sahih al-Bukhari 3038
Sahih al-Bukhari · Book 56: Fighting for the Cause of Allah (Jihaad) · What quarrels and differences are hated in the war
Narrated Abu Burda:
حَدَّثَنَا يَحْيَى ، حَدَّثَنَا وَكِيعٌ ، عَنْ شُعْبَةَ ، عَنْ سَعِيدِ بْنِ أَبِي بُرْدَةَ ، عَنْ أَبِيهِ ، عَنْ جَدِّهِ ، أَنَّ النَّبِيَّ صلى الله عليه وسلم بَعَثَ مُعَاذًا وَأَبَا مُوسَى إِلَى الْيَمَنِ قَالَ " يَسِّرَا وَلاَ تُعَسِّرَا، وَبَشِّرَا وَلاَ تُنَفِّرَا، وَتَطَاوَعَا وَلاَ تَخْتَلِفَا " .
That his father said, "The Prophet (ﷺ) sent Mu`adh and Abu Musa to Yemen telling them. 'Treat the people with ease and don't be hard on them; give them glad tidings and don't fill them with aversion; and love each other, and don't differ."