Qur'ān 39:13 · Az-Zumar (الزمر)

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."