Musnad Ahmad 30:768

Ibn Numayr narrated to us, 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, Jayhan, the Nile, and the Euphrates are all from the rivers of Paradise."