From Sahih Bukhari (Hadith 3244):
Narrated Abu Huraira:Allah's Messenger (ﷺ) said, "Allah said, "I have prepared for My Pious slaves things which have never been seen by an eye, or heard by an ear, or imagined by a human being." If you wish, you can recite this Verse from the Holy Qur'an:--"No soul knows what is kept hidden for them, of joy as a reward for what they used to do
Reference: Bukhari 3244