Musnad Ahmad 30:2521

Yahya ibn Sa'id narrated to us, from Muhammad ibn 'Amr, who said: Abu Salamah narrated to me, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him: "Allah the Exalted 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.' And recite, if you wish: {No soul knows what has been hidden for them of comfort for eyes} [As-Sajdah: 17]."