Musnad Ahmad 30:426

Ibn Numayr and Yazid narrated to us, they said: Muhammad ibn ‘Amr informed us, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Four rivers gushed forth from Paradise: the Euphrates, the Nile, Sayhan, and Jayhan."