It was narrated that Ibn 'Abbas said:
"One of the wives of the Prophet took a bath from a large vessel, then the Prophet came and had a bath or ablution, and she said: 'O Messenger of Allah, I was sexually impure.' He said: 'Water does not become impure.'" (DE)
English reference (DE): Vol. 1, Book 1, Hadith 370 (DE)
Arabic reference (DE): Book 1, Hadith 400 (DE)