Yes, and the Qur'an says so directly: "No! Rather, the stain (rān) has covered their hearts from what they used to earn" (Quran 83:14). Explaining this verse, the Prophet ﷺ said that when a servant sins a black spot is placed on his heart; if he refrains, seeks forgiveness and repents his heart is polished clean, but if he returns to the sin it increases until it covers his whole heart — "and that is the rān which Allah mentioned" (Jāmiʿ at-Tirmidhī 3334, graded ḥasan ṣaḥīḥ by at-Tirmidhī; also Sunan Ibn Mājah 4244). So numbness is not a reason for despair but a warning sign with a known remedy: leave the sin, seek forgiveness, and return to what softens hearts — "Truly, it is in the remembrance of Allah that hearts find rest" (Quran 13:28), along with the Qur'an, the prayer, and keeping good company.
Q&A · Repentance & Sin
Why does my heart feel hard and numb — does sin actually damage the heart?
Evidence — the daleel
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.