كتاب الذكر والدعاء والتوبة والاستغفار
48
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness
(2)
Chapter: The Names Of Allah, Exalted is He, And The Virtue Of The One Who Learns Them By Heart
(2)
باب فِي أَسْمَاءِ اللَّهِ تَعَالَى وَفَضْلِ مَنْ أَحْصَاهَا

Abu Huraira reported Allah's Messenger (ﷺ) as saying:

There are ninety-nine names of Allah; he who commits them to memory would get into Paradise. Verily, Allah is Odd (He is one, and it is an odd number) and He loves odd number. And in the narration of Ibn 'Umar (the words are):" He who enumerated them."
حَدَّثَنَا عَمْرٌو النَّاقِدُ، وَزُهَيْرُ بْنُ حَرْبٍ، وَابْنُ أَبِي عُمَرَ، جَمِيعًا عَنْ سُفْيَانَ، - وَاللَّفْظُ لِعَمْرٍو - حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ لِلَّهِ تِسْعَةٌ وَتِسْعُونَ اسْمًا مَنْ حَفِظَهَا دَخَلَ الْجَنَّةَ وَإِنَّ اللَّهَ وِتْرٌ يُحِبُّ الْوِتْرَ ‏"‏ ‏.‏ وَفِي رِوَايَةِ ابْنِ أَبِي عُمَرَ ‏"‏ مَنْ أَحْصَاهَا ‏"‏ ‏.‏
Reference : Sahih Muslim 2677 a
In-book reference : Book 48, Hadith 5
USC-MSA web (English) reference : Book 35, Hadith 6475
  (deprecated numbering scheme)