The Quran

قُل لا أَملِكُ لِنَفسي ضَرًّا وَلا نَفعًا إِلّا ما شاءَ اللَّهُ ۗ لِكُلِّ أُمَّةٍ أَجَلٌ ۚ إِذا جاءَ أَجَلُهُم فَلا يَستَأخِرونَ ساعَةً ۖ وَلا يَستَقدِمونَ

Muhammad Asad

Say [O Prophet]: "It is not within my power to avert harm from, or bring benefit to, myself, except as God may please.¹ For all people a term has been set: when the end of their term approaches, they can neither delay it by a single moment, nor hasten it."²

Sc., "and since I do not possess any supernatural powers, I cannot predict that which is beyond the reach of human perception (al-ghayb)".
See 7:34 and the corresponding notes 25 and 26. In the above context, the "end of the term" refers, in particular, to the coming of the Last Hour and the Day of Judgment.