Nahj al-Balāgha
Hadith 2009وَالْخَامِسُ: أَنْ تَعْمِدَ إِلَى اللَّحْمِ الَّذِي نَبَتَ عَلَى السُّحْتِ فَتُذِيبَهُ بِالْأَحْزَانِ، حَتَّى يَلْصِقَ الْجِلْدُ بِالْعَظْمِ، وَيَنْشَأَ بَيْنَهُمَا لَحْمٌ جَدِيدٌ.
the fifth is to aim at the flesh grown as a result of unlawful earning, so that you may melt it by grief (of repentance) till the skin touches the bone and a new flesh grows between them;