Musnad Ahmad 30:3293

Ibn Numayr narrated to us, al-A‘mash narrated to us, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: Allah the Exalted says: "I have prepared for My righteous servants what no eye has seen, no ear has heard, and has not occurred to the heart of any human being, as a treasure from that which I have not informed you of." Then he recited: {No soul knows what has been hidden for them of comfort for eyes} [As-Sajdah: 17].