It was narrated that Abu Hurairah said:
"The Messenger of Allah said: 'The (following) was revealed about the people of Quba': 'In it (the mosque) are men who love to clean and purify themselves. And Allah loves those who make themselves clean and pure.'" He said: 'They used to clean themselves with water (after urinating), and this Verse was revealed concerning them.'"
English reference: Vol. 1, Book 1, Hadith 357
Arabic reference: Book 1, Hadith 386