Mishkat al-Masabih #395

‘Abdallah b. ‘Amr b. al-‘As said that the Prophet came upon Sa'd when he was performing ablution and asked, “What is the meaning of this extravagance, Sa'd?” He replied, “Is there extravagance in ablution?” He said, “Yes, even if you are beside a flowing river.’’ Ahmad and Ibn Majah transmitted it.