قُلْ إِنَّمَا ٱلْعِلْمُ عِندَ ٱللَّهِ وَإِنَّمَآ أَنَا۠ نَذِيرٌ مُّبِينٌ
Qul innamal 'ilmu 'indallaahi wa innamaaa ana nazeerum mubeen
Say: the knowledge rests with God alone, and I am only a clear warner.
The reply rests on one restrictive particle used twice, innamā, placing the timing with God and then holding the Messenger's role to the warning itself. A demand for a date is answered by declining the date, which is the consistent line of this surah: knowledge belongs to the one who made hearing and sight, and the schedule was never handed to anyone else.