(a) Sayyidah Aishah (may Allah be pleased with her) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Ten things are part of the fitrah (natural disposition): trimming the moustache, letting the beard grow, using the miswak, sniffing water into the nose, cutting the nails, washing the finger joints, plucking the armpit hair, shaving the pubic hair, and cleaning oneself with water (istinja)." Zakariyya, the narrator, says that Mus'ab said: I have forgotten the tenth; perhaps it is rinsing the mouth.
(b) The wording of the narration in Sahih Muslim is: "cleaning oneself with water (istinja)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 241