It is narrated from Sayyidah Aishah (may Allah be pleased with her) 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 siwak, sniffing water into the nose and blowing it out, clipping the nails, washing the finger joints, plucking the armpit hair, shaving the pubic hair, and pouring water (for cleaning)." Mus'ab said: I forgot the tenth, (it may be that) it is rinsing the mouth.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 153