It is narrated from Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him), describing Paradise, said: "In it is what no eye has seen, no ear has heard, and has never occurred to the heart of any human being."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5979
Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) relates that we were with the Messenger of Allah (peace and blessings be upon him) while he was describing Paradise, until he reached this point and said: "In it is what no eye has seen, no ear has heard, and has never occurred to the heart of any human being." Then he (peace and blessings be upon him) recited this verse: "Their sides forsake their beds (at night); they call upon their Lord in fear and hope, and they spend out of what We have provided them" [Surah al-Sajdah: 16], up to the verse: "as a reward for what they used to do" [Surah al-Sajdah: 17].
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5980