Will Allah forgive one who commits a sin that causes his illness, and will he gain good deeds thereby?

It is not permissible for a Muslim to undertake anything that harms his health, based on the Almighty's saying: "And do not kill yourselves. Indeed, Allah is ever Merciful to you." (Quran 4:29). Whoever does something that causes illness unintentionally is not held accountable, for Allah has pardoned what occurs by mistake or out of forgetfulness. A Muslim is rewarded for any illness or distress that befalls him. Whoever intentionally commits a sin should hasten to repent, for Allah accepts the repentance of the sincere and rejoices in it, as affirmed by His saying: "And whoever does evil or wrongs himself but then seeks Allah’s forgiveness will find Allah Forgiving and Merciful." (Quran 4:110) and His saying: "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" (Quran 39:53).