(a) Sayyiduna Ibn Abbas (may Allah be pleased with them both) said concerning the saying of Allah, "And when his Lord tested Ibrahim with certain words" [Surah al-Baqarah: 124]: Allah Almighty tested him with (matters of) purification: five relate to the head and five to the body. Those of the head are: trimming the moustache, rinsing the mouth, sniffing water into the nose, using the tooth-stick (miswak), and parting the hair. Those of the body are: clipping the nails, shaving the pubic hair, circumcision, plucking the armpit hair, and washing the places of defecation and urination with water.
(b) Sayyidah Aishah (may Allah be pleased with her) narrated from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "Ten things are part of the fitrah (natural disposition)," then he mentioned them, and he also mentioned letting the beard grow and washing the finger joints, but did not mention circumcision and parting the hair.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 685