Surah Al-An'am 6:15

قُلْ إِنِّىٓ أَخَافُ إِنْ عَصَيْتُ رَبِّى عَذَابَ يَوْمٍ عَظِيمٍ

Say, "Indeed I fear, if I should disobey my Lord, the punishment of a tremendous Day."

Translation: Saheeh International

Tafsir

Say ‘Indeed I fear if I should rebel against my Lord by worshipping other than Him the chastisement of a dreadful day’ namely the Day of Resurrection.

Excerpt from Tafsir al-Jalalayn, commentary on 6:15, via Quran.com. The reader has the full commentary and 9 more tafsirs.