Musnad Ahmad 30:2546

Ibn Numayr and Abu Usamah narrated to us, they said: Ubaydullah narrated to us, from Khubayb ibn Abd al-Rahman, from Hafs ibn Asim, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Sayhan and Jayhan, and the Nile and the Euphrates, are all from the rivers of Paradise." Abu Usamah said: "All are from the rivers of Paradise."