Nahj al-Balāgha
Hadith 1473وَأَمَرَهُ أَنْ يَكْسِرَ نَفْسَهُ مِنَ الشَّهَوَاتِ، وَيَزَعَهَا عِنْدَ الْجَمَحَاتِ، فَإِنَّ النَّفْسَ أَمَّارَةٌ بِالسُّوءِ، إِلَّا مَا رَحِمَ اللهُ.
He also orders him to break his heart off from passions, and to restrain it at the time of their increase, because the heart leads towards evil unless Allāh has mercy.