Musannaf Ibn Abi Shayba 1:1631

Hafs narrated to us, from Dawud, from Ibn Abi Layla, from al-Sha'bi, who said: When this verse was revealed: "Therein are men who love to purify themselves, and Allah loves those who purify themselves," the Messenger of Allah (peace be upon him) said: "O people of Quba, what is this praise with which Allah has praised you?" They said: "There is not one of us except that he cleans himself with water after relieving himself."