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