Surah 39. Az-Zumar, Ayah 53

See note [16] on the opening words of verse {10} of this surah {11}.

Sc.. "whenever the sinner repents and turns to Him": cf., for instance, 6:54 - "Your Sustainer has willed upon Himself the law of grace and mercy - so that if any of you does a bad deed out of ignorance, and thereafter repents and lives righteously, He shall be [found] muchforgiving, a dispenser of grace"; or 4:110 - "he who does evil or [otherwise] sins against himself, and thereafter prays God to forgive him, shall find God much-forgiving, a dispenser of grace".

 No matter how big someone’s sins are, they cannot be bigger than Allah’s mercy. Based on 4:48, the only unforgivable sin in Islam is if someone dies while disbelieving in Allah or associating others with Him in worship. In an authentic narration collected by At-Tirmiⱬi, the Prophet (ﷺ) reports that Almighty Allah says, "O children of Adam! As long as you call upon Me, putting your hope in Me, I will forgive you for what you have done, and I will not mind. O  children of Adam! If your sins were to reach the clouds of the sky and then you sought My forgiveness, I would ˹still˺ forgive you. O  children of Adam! If you were to come to Me with sins filling the whole world and then you came to Me without associating other gods with Me, I would certainly match your sins with forgiveness."

Forgives all sins: i.e., on sincere repentance and amendment of conduct.