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.'" (JA)
English reference (JA): Vol. 1, Book 1, Hadith 421 (JA)
Arabic reference (JA): Book 1, Hadith 456 (JA)