Musnad Ahmad 30:2887

'Abd al-Rahman ibn Mahdi narrated to us, Sufyan narrated to us, from al-A'mash, from Abu Salih, from Abu Hurayrah, that the Prophet, peace and blessings of Allah be upon him, said: "Allah, the Almighty and Majestic, said: '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.'"