Heaviest on the scale

Nothing is heavier on the scale than good character.

Narrated by Abu ad-Darda

Nothing is heavier on the scale of the believer on the Day of Resurrection than good character.

Jami' at-Tirmidhi 2002, Sunan Abi Dawud 4799

What this hadith teaches

Good manners can outweigh many voluntary acts.

Reference and grade

Grade
Sahih (al-Albani)
Narrator
Abu ad-Darda

The hadith in Arabic نص الحديث

مَا شَيْءٌ أَثْقَلُ فِي مِيزَانِ الْمُؤْمِنِ يَوْمَ الْقِيَامَةِ مِنْ خُلُقٍ حَسَنٍ وَإِنَّ اللَّهَ لَيَبْغَضُ الْفَاحِشَ الْبَذِيءَ

Arabic text of Jami' at-Tirmidhi 2002, as given on sunnah.com.