Musnad Ahmad 30:2378

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Abu Sufyan, from Jabir, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The likeness of the five prayers is like a flowing river, deep, at the door of one of you; he bathes in it five times every day."