Narrated Abu Huraira: Allah's Apostle 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.
Hadith ReferenceSahih Bukhari / The Book of Tauhid (Islamic Monotheism) / Hadith: 7392
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة