The Messenger of Allah ﷺ said, "Allah has ninety-nine names, one hundred less one. Whoever enumerates them all will enter Paradise."
حدثنا إسماعيل عن هشام ويزيد يعني ابن هارون قال أخبرنا هشام عن ابن سيرين
قال رسول الله ﷺ لله عز وجل تسعة وتسعون اسما مائة إلا واحدا من أحصاها كلها دخل الجنة
Its isnad is sahih. Bukhari related it, 3/259, in "Conditions," the chapter on what stipulations and exceptions are permissible, and Muslim, 4/2063, no. 2977, in "Remembrance," the chapter on the names of Allah Almighty, and Tirmidhi, 5/530, no. 3506, in "Supplications," the chapter on what has been said about counting tasbih on the hand, and he graded it sahih, and Ibn Majah, 2/1269, no. 3860.