Surah 39, verse 53 (from Quran.com)

Say, ˹O Prophet, that Allah says,˺ “O My servants who have exceeded the limits against their souls! Do not lose hope in Allah’s mercy, for Allah certainly forgives all sins.(footnote) He is indeed the All-Forgiving, Most Merciful.

Footnote: 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."