Verily, Allah has ninety-nine names, one-hundred minus one. Whoever memorizes them all will enter Paradise
Authentic hadithعن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال: «إن لله تِسْعَةً، وتِسْعِينَ، اسْمًا، مِائَةً إلا واحدا مَنْ أَحْصَاهَا دخل الجنة».
Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Verily, Allah has ninety-nine names, one-hundred minus one. Whoever memorizes them all will enter Paradise."
Explanation
This Hadīth states that Allah, the Almighty, has ninety-nine names, and that whoever memorizes them all, believes in their meanings, and acts according to their implications, in matters other than those reserved exclusively for Allah, the Almighty, will enter Paradise. Making an oath by any of these names is permissible and binding. Consequently, one must offer expiation if he broke an oath sworn by one of the names of Allah, the Most Merciful and the Ever Merciful, or by one of His attributes such as His Face, Greatness, Grandeur, and Might.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).