It was narrated that Ubayy bin Ka'b said:
"The Messenger of Allah said: 'There is a devil for ablution who is called Walahan, so be on guard against the insinuating thoughts (Waswas) about water.'" (DE)
English reference (DE): Vol. 1, Book 1, Hadith 421 (DE)
Arabic reference (DE): Book 1, Hadith 456 (DE)