Allah the Exalted said,

قُلْ إِنَّ الْأَوَّلِينَ وَالْآخِرِينَ ﴿٤٩﴾

لَمَجْمُوعُونَ إِلَى مِيقَاتِ يَوْمٍ مَّعْلُومٍ ﴿٥٠﴾

Say:

"(Yes) verily, those of old, and those of later times. All will surely be gathered together for appointed meeting of a known Day.''

meaning, `Say, O Muhammad, that the earlier and latter generations of the Children of Adam will be gathered for the Day of Resurrection and none of them will be left out.

Allah the Exalted said:

ذلِكَ يَوْمٌ مَّجْمُوعٌ لَّهُ النَّاسُ وَذَلِكَ يَوْمٌ مَّشْهُودٌ

وَمَا نُؤَخِّرُهُ إِلاَّ لاًّجَلٍ مَّعْدُودٍ

يَوْمَ يَأْتِ لاَ تَكَلَّمُ نَفْسٌ إِلاَّ بِإِذْنِهِ فَمِنْهُمْ شَقِىٌّ وَسَعِيدٌ

That is a Day whereon mankind will be gathered together, and that is a Day when all will be present. And We delay it only for a term fixed. On the Day when it comes, no person shall speak except by His leave. Some among them will be wretched and (others) blessed. (11:103-105)

He also said here,

لَمَجْمُوعُونَ إِلَى مِيقَاتِ يَوْمٍ مَّعْلُوم

All will surely be gathered together for appointed meeting of a known Day.

because that time is precisely designated and will not come late, early, nor increase or decrease.