Musannaf Ibn Abi Shayba 3:5274

Muhammad ibn Ubayd narrated to us, from al-A’mash, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The likeness of the five daily prayers is only like a flowing river at the door of one of you, in which he bathes five times every day. Does any of his filth remain?"