That you not worship except Allah. Indeed, I fear for you the punishment of a painful day."
The Saheeh International Quran Translation
أَن لَّا تَعْبُدُوٓا۟ إِلَّا ٱللَّهَ إِنِّىٓ أَخَافُ عَلَيْكُمْ عَذَابَ يَوْمٍ أَلِيمٍThat you not worship except Allah. Indeed, I fear for you the punishment of a painful day."