The Prophet صلى الله عليه وسلم said:

مَا مِنْ شَيْءٍ أَثْقَلُ فِي الْمِيزَانِ مِنْ حُسْنِ الْخُلُق

"There is nothing heavier than good character put in the scale of a believer (on the Day of Resurrection)"

(Sunan Abu-Dawud # 4166)