Qur'ān 6:15 · Al-An'am (الأنعام)

قُلْ إِنِّىٓ أَخَافُ إِنْ عَصَيْتُ رَبِّى عَذَابَ يَوْمٍ عَظِيمٍۢ

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