Musnad Ahmad 30:3350

'Ali ibn 'Asim narrated to us, Khalid and Hisham informed us, from Muhammad ibn Sirin, from Abu Hurayrah, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Indeed, Allah, the Almighty and Majestic, has ninety-nine names. Whoever enumerates them all will enter Paradise."