Sayyiduna Ibn Umar (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) said: "When it is the seventh day of his (the newborn's) life, shed blood on his behalf (perform the aqiqah), and remove the harmful thing (the hair) from him."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13135