Quran 18:23 from Surah Al-Kahf on Divine Marvels.
وَلَا تَقُولَنَّ لِشَاْيۡءٍ إِنِّي فَاعِلٞ ذَٰلِكَ غَدًا
English translation: And (do) not say of anything Indeed I will do that tomorrow
Transliteration: wala taqulanna lishay'in inni fa'ilun dhalika ghadan