Umm Darda reported: Abu Darda, may Allah be pleased with them both, stood praying and weeping, saying, “O Allah, you have made my form excellent, so make my character excellent.” He continued until the morning and I said, “O Abu Darda, you did not supplicate for anything but good character!” Abu Darda said, “O Umm Darda, the Muslim servant will make his character excellent until he enters Paradise by his good character, and he will make his character wicked until he enters Hellfire by his evil character.”
Source: al-Karam wal-Jūd 19
عَنْ أُمِّ الدَّرْدَاءِ قَالَتْ قَامَ أَبُو الدَّرْدَاءِ رضي الله عنهما يُصَلِّي فَجَعَلَ يَبْكِي وَيَقُولُ اللَّهُمَّ حَسَّنْتَ خَلْقِي فَحَسِّنْ خُلْقِي حَتَّى أَصْبَحَ قَالَتْ أُمُّ الدَّرْدَاءِ فَقُلْتُ يَا أَبَا الدَّرْدَاءِ مَا كَانَ دُعَاؤُكَ اللَّيْلَةَ إِلَّا فِي حُسْنِ الْخُلُقِ فَقَالَ يَا أُمَّ الدَّرْدَاءِ إِنَّ الْعَبْدَ الْمُسْلِمَ يُحَسِّنُ خُلُقَهُ حَتَّى يُدْخِلَهُ حُسْنُ خُلُقِهِ الْجَنَّةَ وَإِنَّهُ لَيُسِيءُ خُلُقَهُ حَتَّى يُدْخِلَهُ سُوءُ خُلُقِهِ النَّارَ
19 الكرم والجود للبرجلاني