Messenger of Allah ﷺ said, "Allah has ninety-nine Names, one-hundred less one; and he who memorized them all by heart will enter Paradise." To count something means to know it by heart.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ لِلَّهِ تِسْعَةً وَتِسْعِينَ اسْمًا مِائَةً إِلاَّ وَاحِدًا مَنْ أَحْصَاهَا دَخَلَ الْجَنَّةَ {أَحْصَيْنَاهُ} حَفِظْنَاهُ