Quran 11:26 from Surah Hud on Divine Marvels.
أَن لَّا تَعۡبُدُوٓاْ إِلَّا ٱللَّهَۖ إِنِّيٓ أَخَافُ عَلَيۡكُمۡ عَذَابَ يَوۡمٍ أَلِيمٖ
English translation: That (do) not worship except Allah Indeed I [I] fear for you (the) punishment (of) a Day painful
Transliteration: an la ta'budu illa al-laha inni akhafu alaykum adhaba yawmin alimin