(a) It is narrated from Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) that he (peace and blessings be upon him) said: "Indeed, ablution too has a devil who is called al-Walhan, so beware of him," or he said: "Fear him."
(b) In one narration it says: "Beware of him, and fear the whispering (waswasah) of water."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 948