Surah Al-Qasas 28:16

قَالَ رَبِّ إِنِّى ظَلَمْتُ نَفْسِى فَٱغْفِرْ لِى فَغَفَرَ لَهُۥٓ ۚ إِنَّهُۥ هُوَ ٱلْغَفُورُ ٱلرَّحِيمُ

He said, "My Lord, indeed I have wronged myself, so forgive me," and He forgave him. Indeed, He is the Forgiving, the Merciful.

Translation: Saheeh International

Tafsir

He said remorsefully ‘My Lord I have indeed wronged myself by killing him so forgive me!’ So He forgave him. Truly He is the Forgiving the Merciful that is to say the One Who has always possessed and will always possess these two attributes.

Excerpt from Tafsir al-Jalalayn, commentary on 28:16, via Quran.com. The reader has the full commentary and 9 more tafsirs.