Musnad Ahmad 33:163

Muhammad ibn Fudayl narrated to us, al-A'mash narrated to us, from Abu Sufyan, from Jabir, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "The likeness of the five prescribed prayers is like a flowing river at the door of one of you, in which he bathes five times every day."